# Acegi Security System for Spring

## Reference Documentation

### Ben Alex

1.0.0 RC 1

## Preface

This document provides a reference guide to the Acegi Security System for Spring, which is a series of classes that deliver authentication and authorization services within the Spring Framework.

I would like to acknowledge this reference was prepared using the DocBook configuration included with the Spring Framework. The Spring team in turn acknowledge Chris Bauer (Hibernate) for his assistance with their DocBook.

## Chapter 1. Security

## 1.1. Before You Begin

For your security, each official release JAR of Acegi Security has been signed by the project leader. This does not in any way alter the liability disclaimer contained in the License, but it does ensure you are using a properly reviewed, official build of Acegi Security. Please refer to the `readme.txt` file in the root of the release distribution for instructions on how to validate the JARs are correctly signed, and which certificate has been used to sign them.

## 1.2. Introduction

The Acegi Security System for Spring provides authentication and authorization capabilities for Spring-powered projects, with optional integration with popular web containers. The security architecture was designed from the ground up using "The Spring Way" of development, which includes using bean contexts, interceptors and interface-driven programming. As a consequence, the Acegi Security System for Spring is useful out-of-the-box for those seeking to secure their Spring-based applications, and can be easily adapted to complex customized requirements.

Security involves two distinct operations, authentication and authorization. The former relates to resolving whether or not a caller is who they claim to be. Authorization on the other hand relates to determining whether or not an authenticated caller is permitted to perform a given operation.

Throughout the Acegi Security System for Spring, the user, system or agent that needs to be authenticated is referred to as a "principal". The security architecture does not have a notion of roles or groups, which you may be familiar with from other security implementations, although equivalent functionality is fully accommodated by Acegi Security.

### 1.2.1. Current Status

The Acegi Security System for Spring is widely used by members of the Spring Community. The APIs are considered stable and only minor changes are expected. Having said that, like many other projects we need to strike a balance between backward compatibility and improvement. Effective version 0.6.1, Acegi Security uses the Apache Portable Runtime Project versioning guidelines, available from `http://apr.apache.org/versioning.html`.

We are now at release 0.9.0, and a lot of effort has been made to implement all non-backward compatible changes either in or before this release. Some minor improvements are currently intended to the 1.0.0 release, although they will in no way modify the project's central interfaces or classes. Users of Acegi Security System for Spring should therefore be comfortable depending on the current version of the project in their applications. Please note that we will be changing the package name prefix in the 1.0.0 release, but this should be a simple "find and replace" type operation in your code.

## 1.3. High Level Design

### 1.3.1. Key Components

Most enterprise applications have four basic security requirements. First, they need to be able to authenticate a principal. Second, they need to be able to secure web requests. Third, enterprise applications need to be able to secure services layer methods. Finally, quite often an enterprise application will need to secure domain object instances. Acegi Security provides a comprehensive framework for achieving all of these four common enterprise application security requirements.

The Acegi Security System for Spring essentially comprises eight key functional parts:

- An `Authentication` object which holds the principal, credentials and the authorities granted to the principal. The object can also store additional information associated with an authentication request, such as the source TCP/IP address.

- A `SecurityContextHolder` which holds the `Authentication` object in a `ThreadLocal`-bound object.

- An `AuthenticationManager` to authenticate the `Authentication` object presented via the `ContextHolder`.

- An `AccessDecisionManager` to authorize a given operation.

- A `RunAsManager` to optionally replace the `Authentication` object whilst a given operation is being executed.

- A "secure object" interceptor, which coordinates the authentication, authorization, run-as replacement, after invocation handling and execution of a given operation.

- An `AfterInvocationManager` which can modify an `Object` returned from a "secure object" invocation, such as removing `Collection` elements a principal does not have authority to access.

- An acess control list (ACL) management package, which can be used to obtain the ACLs applicable for domain object instances.

A "secure object" interceptor executes most of the Acegi Security key classes and in doing so delivers the framework's major features. Given its importance, Figure 1 shows the key relationships and concrete implementations of `AbstractSecurityInterceptor`.

Figure 1: The key "secure object" model

Each "secure object" interceptor (hereinafter called a "security interceptor") works with a particular type of "secure object". So, what is a secure object? Secure objects refer to any type of object that can have security applied to it. A secure object must provide some form of callback, so that the security interceptor can transparently do its work as required, and callback the object when it is time for it to proceed with the requested operation. If secure objects cannot provide a native callback approach, a wrapper needs to be written so this becomes possible.

Each secure object has its own package under `org.acegisecurity.intercept`. Every other package in the security system is secure object independent, in that it can support any type of secure object presented.

Only developers contemplating an entirely new way of intercepting and authorizing requests would need to use secure objects directly. For example, it would be possible to build a new secure object to secure calls to a messaging system that does not use `MethodInvocation`s. Most Spring applications will simply use the three currently supported secure object types (AOP Alliance `MethodInvocation`, AspectJ `JoinPoint` and web request `FilterInterceptor`) with complete transparency.

Each of the eight key parts of Acegi Security are discussed in detail throughout this document.

### 1.3.2. Supported Secure Objects

As shown in the base of Figure 1, the Acegi Security System for Spring currently supports three secure objects.

The first handles an AOP Alliance `MethodInvocation`. This is the secure object type used to protect Spring beans. Developers will generally use this secure object type to secure their business objects. To make a standard Spring-hosted bean available as a `MethodInvocation`, the bean is simply published through a `ProxyFactoryBean` or `BeanNameAutoProxyCreator` or `DefaultAdvisorAutoProxyCreator`. Most Spring developers would already be familiar with these due to their use in transactions and other areas of Spring.

The second type is an AspectJ `JoinPoint`. AspectJ has a particular use in securing domain object instances, as these are most often managed outside the Spring bean container. By using AspectJ, standard constructs such as `new Person();` can be used and full security will be applied to them by Acegi Security. The `AspectJSecurityInterceptor` is still managed by Spring, which creates the aspect singleton and wires it with the appropriate authentication managers, access decision managers and so on.

The third type is a `FilterInvocation`. This is an object included with the Acegi Security System for Spring. It is created by an included filter and simply wraps the HTTP `ServletRequest`, `ServletResponse` and `FilterChain`. The `FilterInvocation` enables HTTP resources to be secured. Developers do not usually need to understand the mechanics of how this works, because they just add the filters to their `web.xml` and let the security system do its work.

### 1.3.3. Configuration Attributes

Every secure object can represent an infinite number of individual requests. For example, a `MethodInvocation` can represent the invocation of any method with any arguments, whilst a `FilterInvocation` can represent any HTTP URL.

The Acegi Security System for Spring needs to record the configuration that applies to each of these possible requests. The security configuration of a request to `BankManager.getBalance(int accountNumber)` needs to be very different from the security configuration of a request to `BankManager.approveLoan(int applicationNumber)`. Similarly, the security configuration of a request to `http://some.bank.com/index.htm` needs to be very different from the security configuration of `http://some.bank.com/manage/timesheet.jsp`.

To store the various security configurations associated with different requests, a configuration attribute is used. At an implementation level a configuration attribute is represented by the `ConfigAttribute` interface. One concrete implementation of `ConfigAttribute` is provided, `SecurityConfig`, which simply stores a configuration attribute as a `String`.

The collection of `ConfigAttribute`s associated with a particular request is held in a `ConfigAttributeDefinition`. This concrete class is simply a holder of `ConfigAttribute`s and does nothing special.

When a request is received by the security interceptor, it needs to determine which configuration attributes apply. In other words, it needs to find the `ConfigAttributeDefinition` which applies to the request. This decision is handled by the `ObjectDefinitionSource` interface. The main method provided by this interface is `public ConfigAttributeDefinition getAttributes(Object object)`, with the `Object` being the secure object. Recall the secure object contains details of the request, so the `ObjectDefinitionSource` implementation will be able to extract the details it requires to lookup the relevant `ConfigAttributeDefinition`.

## 1.4. Request Contexts

### 1.4.1. Historical Approach

Prior to release 0.9.0, Acegi Security used a `ContextHolder` to store a `Context` between sessions. A particular subclass of `Context`, `SecureContext` defined an interface used for storage of the `Authentication` object. The `ContextHolder` was a `ThreadLocal`. A fuller discussion of the `ThreadLocal` usage with Acegi Security follows in this document. `ContextHolder` and `SecureContext` was removed from 0.9.0 after discussion with other Spring developers for the sake of consistency. See for example `http://article.gmane.org/gmane.comp.java.springframework.devel/8290` and JIRA task SEC-77. This history is mentioned as the long period `ContextHolder` was used will likely mean that certain documentation you encounter concerning Acegi Security might still refer to `ContextHolder`. Generally you can just substitute "`SecurityContextHolder`" for "`ContextHolder`", and "`SecurityContext`" for "`SecureContext`", and you'll have the primary meaning of such documentation.

### 1.4.2. SecurityContext

The Acegi Security System for Spring uses a `SecurityContextHolder` to store the `SecurityContext`. The `SecurityContext` contains a single getter/setter for `Authentication`. All Acegi Security classes query the `SecurityContextHolder` for obtaining the current `SecurityContext` (and in turn the principal). `SecurityContextHolder` is a `ThreadLocal`, meaning it is associated with the current thread of execution.

### 1.4.3. Context Storage

Central to Acegi Security's design is that the contents of the `SecurityContextHolder` (which is simply a `SecurityContext` implementation) can be stored between web requests. This is so that a successfully authenticated principal can be identified on subsequent requests through the `Authentication` stored inside the `SecurityContext` obtained from the `SecurityContextHolder`. The `HttpSessionContextIntegrationFilter` exists to automatically copy the contents of a well-defined `HttpSession` attribute into the `SecurityContextHolder`, then at the end of each request, copy the `SecurityContextHolder` contents back into the `HttpSession` ready for next request.

It is essential - and an extremely common error of end users - that `HttpSessionContextIntegrationFilter` appears before any other Acegi Security filter. Acegi Security filters expect to be able to modify the `SecurityContextHolder` contents as they see fit, and something else (namely `HttpSessionContextIntegrationFilter`) will store those between requests if necessary. This is why `HttpSessionContextIntegrationFilter` must be the first filter used.

You can define a custom `SecurityContext` implementation be used in your application by setting the `context` property on the `HttpSessionContextIntegrationFilter` bean.

### 1.4.4. Localization

From 1.0.0, Acegi Security supports localization of exception messages that end users are likely to see. Such exceptions include authentication failures and access being denied (authorization failures). Exceptions and logging that is focused on developers or system deployers (including incorrect attributes, interface contract violations, using incorrect constructors, startup time validation, debug-level logging) etc are not localized and instead are hard-coded in English within Acegi Security's code.

Shipping in the `acegi-security-xx.jar` inside the `org.acegisecurity` package is a `messages.properties` file. This should be referred to by your `ApplicationContext`, as Acegi Security classes implement Spring's `MessageSourceAware` interface and expect the message resolver to be dependency injected at application context startup time. Usually all you need to do is register a bean inside your application context to refer to the messages. An example is shown below:

    <bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
      <property name="basename"><value>org/acegisecurity/messages</value></property>
    </bean>

The `messages.properties` is named in accordance with standard resource bundles and represents the default language supported by Acegi Securtiy messages. This default file is in English. If you do not register a message source, Acegi Security will still work correctly and fallback to hard-coded English versions of the messages.

If you wish to customize the `messages.properties` file, or support other languages, you should copy the file, rename it accordingly, and register it inside the above bean definition. There are not a large number of message keys inside this file, so localization should not be considered a major initiative. If you do perform localization of this file, please consider sharing your work with the community by logging a JIRA task and attaching your appropriately-named localized version of `messages.properties`.

Rounding out the discussion on localization is the Spring `ThreadLocal` known as `org.springframework.context.i18n.LocaleContextHolder`. You should set the `LocaleContextHolder` to represent the preferred `Locale` of each user. Acegi Security will attempt to locate a message from the message source using the `Locale` obtained from this `ThreadLocal`. Please refer to Spring documentation for further details on using `LocaleContextHolder` and the helper classes that can automatically set it for you (eg `AcceptHeaderLocaleResolver`, `CookieLocaleResolver`, `FixedLocaleResolver`, `SessionLocaleResolver` etc)

## 1.5. Security Interception

### 1.5.1. All Secure Objects

As described in the High Level Design section, each secure object has its own security interceptor which is responsible for handling each request. Handling involves a number of operations:

1. Store the configuration attributes that are associated with each secure request.

2. Extract the `ConfigAttributeDefinition` that applies to the request from the relevant `ObjectDefinitionSource`.

3. Obtain the `Authentication` object from the `SecurityContext`, which is held in the `SecurityContextHolder`.

4. Pass the `Authentication` object to the `AuthenticationManager`, update the `SecurityContextHolder` with the response.

5. Pass the `Authentication` object, the `ConfigAttributeDefinition`, and the secure object to the `AccessDecisionManager`.

6. Pass the `Authentication` object, the `ConfigAttributeDefinition`, and the secure object to the `RunAsManager`.

7. If the `RunAsManager` returns a new `Authentication` object, update the `SecurityContextHolder` with it.

8. Proceed with the request execution of the secure object.

9. If the `RunAsManager` earlier returned a new `Authentication` object, update the `SecurityContextHolder` with the `Authentication` object that was previously returned by the `AuthenticationManager`.

10. If an `AfterInvocationManager` is defined, pass it the result of the secure object execution so that it may throw an `AccessDeniedException` or mutate the returned object if required.

11. Return any result received from the `AfterInvocationManager`, or if no `AfterInvocationManager` is defined, simply return the result provided by the secure object execution.

Whilst this may seem quite involved, don't worry. Developers interact with the security process by simply implementing basic interfaces (such as `AccessDecisionManager`), which are fully discussed below.

The `AbstractSecurityInterceptor` handles the majority of the flow listed above. As shown in Figure 1, each secure object has its own security interceptor which subclasses `AbstractSecurityInterceptor`. Each of these secure object-specific security interceptors are discussed below.

### 1.5.2. AOP Alliance (MethodInvocation) Security Interceptor

To secure `MethodInvocation`s, developers simply add a properly configured `MethodSecurityInterceptor` into the application context. Next the beans requiring security are chained into the interceptor. This chaining is accomplished using Spring’s `ProxyFactoryBean` or `BeanNameAutoProxyCreator`, as commonly used by many other parts of Spring (refer to the sample application for examples). Alternatively, Acegi Security provides a `MethodDefinitionSourceAdvisor` which may be used with Spring's `DefaultAdvisorAutoProxyCreator` to automatically chain the security interceptor in front of any beans defined against the `MethodSecurityInterceptor`. The `MethodSecurityInterceptor` itself is configured as follows:

    <bean id="bankManagerSecurity" class="org.acegisecurity.intercept.method.aopalliance.MethodSecurityInterceptor">
      <property name="validateConfigAttributes"><value>true</value></property>
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="afterInvocationManager"><ref bean="afterInvocationManager"/></property>
      <property name="objectDefinitionSource">
        <value>
          org.acegisecurity.context.BankManager.delete*=ROLE_SUPERVISOR,RUN_AS_SERVER
          org.acegisecurity.context.BankManager.getBalance=ROLE_TELLER,ROLE_SUPERVISOR,BANKSECURITY_CUSTOMER,RUN_AS_SERVER
        </value>
      </property>
    </bean>

As shown above, the `MethodSecurityInterceptor` is configured with a reference to an `AuthenticationManager`, `AccessDecisionManager` and `RunAsManager`, which are each discussed in separate sections below. In this case we've also defined an `AfterInvocationManager`, although this is entirely optional. The `MethodSecurityInterceptor` is also configured with configuration attributes that apply to different method signatures. A full discussion of configuration attributes is provided in the High Level Design section of this document.

The `MethodSecurityInterceptor` can be configured with configuration attributes in three ways. The first is via a property editor and the application context, which is shown above. The second is via defining the configuration attributes in your source code using Jakarta Commons Attributes or Java 5 Annotations. The third is via writing your own `ObjectDefinitionSource`, although this is beyond the scope of this document. Irrespective of the approach used, the `ObjectDefinitionSource` is responsible for returning a `ConfigAttributeDefinition` object that contains all of the configuration attributes associated with a single secure method.

It should be noted that the `MethodSecurityInterceptor.setObjectDefinitionSource()` method actually expects an instance of `MethodDefinitionSource`. This is a marker interface which subclasses `ObjectDefinitionSource`. It simply denotes the `ObjectDefinitionSource` understands `MethodInvocation`s. In the interests of simplicity we'll continue to refer to the `MethodDefinitionSource` as an `ObjectDefinitionSource`, as the distinction is of little relevance to most users of the `MethodSecurityInterceptor`.

If using the application context property editor approach (as shown above), commas are used to delimit the different configuration attributes that apply to a given method pattern. Each configuration attribute is assigned into its own `SecurityConfig` object. The `SecurityConfig` object is discussed in the High Level Design section.

If you are using the Jakarta Commons Attributes approach, your bean context will be configured differently:

    <bean id="attributes" class="org.springframework.metadata.commons.CommonsAttributes"/>
    <bean id="objectDefinitionSource" class="org.acegisecurity.intercept.method.MethodDefinitionAttributes">
      <property name="attributes"><ref local="attributes"/></property>
    </bean>

    <bean id="bankManagerSecurity" class="org.acegisecurity.intercept.method.aopalliance.MethodSecurityInterceptor">
      <property name="validateConfigAttributes"><value>false</value></property>
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="objectDefinitionSource"><ref bean="objectDefinitionSource"/></property>
    </bean>

In addition, your source code will contain Jakarta Commons Attributes tags that refer to a concrete implementation of `ConfigAttribute`. The following example uses the `SecurityConfig` implementation to represent the configuration attributes, and results in the same security configuration as provided by the property editor approach above:

    public interface BankManager {

        /**
         * @@SecurityConfig("ROLE_SUPERVISOR")
         * @@SecurityConfig("RUN_AS_SERVER")
         */
        public void deleteSomething(int id);

        /**
         * @@SecurityConfig("ROLE_SUPERVISOR")
         * @@SecurityConfig("RUN_AS_SERVER")
         */
        public void deleteAnother(int id);

        /**
         * @@SecurityConfig("ROLE_TELLER")
         * @@SecurityConfig("ROLE_SUPERVISOR")
         * @@SecurityConfig("BANKSECURITY_CUSTOMER")
         * @@SecurityConfig("RUN_AS_SERVER")
         */
        public float getBalance(int id);
    }

If you are using the Spring Security Java 5 Annotations approach, your bean context will be configured as follows:

    <bean id="attributes" class="org.acegisecurity.annotation.SecurityAnnotationAttributes"/>
    <bean id="objectDefinitionSource" class="org.acegisecurity.intercept.method.MethodDefinitionAttributes">
      <property name="attributes"><ref local="attributes"/></property>
    </bean>

    <bean id="bankManagerSecurity" class="org.acegisecurity.intercept.method.aopalliance.MethodSecurityInterceptor">
      <property name="validateConfigAttributes"><value>false</value></property>
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="objectDefinitionSource"><ref bean="objectDefinitionSource"/></property>
    </bean>

In addition, your source code will contain the Acegi Java 5 Security Annotations that represent the `ConfigAttribute`. The following example uses the `@Secured` annotations to represent the configuration attributes, and results in the same security configuration as provided by the property editor approach:

    import org.acegisecurity.annotation.Secured;

    public interface BankManager {

        /**
         * Delete something
         */
        @Secured({"ROLE_SUPERVISOR","RUN_AS_SERVER" })
        public void deleteSomething(int id);

        /**
         * Delete another
         */
        @Secured({"ROLE_SUPERVISOR","RUN_AS_SERVER" })
        public void deleteAnother(int id);

        /**
         * Get balance
         */
        @Secured({"ROLE_TELLER","ROLE_SUPERVISOR","BANKSECURITY_CUSTOMER","RUN_AS_SERVER" })
        public float getBalance(int id);
    }

You might have noticed the `validateConfigAttributes` property in the above `MethodSecurityInterceptor` examples. When set to `true` (the default), at startup time the `MethodSecurityInterceptor` will evaluate if the provided configuration attributes are valid. It does this by checking each configuration attribute can be processed by either the `AccessDecisionManager` or the `RunAsManager`. If neither of these can process a given configuration attribute, an exception is thrown. If using the Jakarta Commons Attributes method of configuration, you should set `validateConfigAttributes` to `false`.

### 1.5.3. AspectJ (JoinPoint) Security Interceptor

The AspectJ security interceptor is very similar to the AOP Alliance security interceptor discussed in the previous section. Indeed we will only discuss the differences in this section.

The AspectJ interceptor is named `AspectJSecurityInterceptor`. Unlike the AOP Alliance security interceptor, which relies on the Spring application context to weave in the security interceptor via proxying, the `AspectJSecurityInterceptor` is weaved in via the AspectJ compiler. It would not be uncommon to use both types of security interceptors in the same application, with `AspectJSecurityInterceptor` being used for domain object instance security and the AOP Alliance `MethodSecurityInterceptor` being used for services layer security.

Let's first consider how the `AspectJSecurityInterceptor` is configured in the Spring application context:

    <bean id="bankManagerSecurity" class="org.acegisecurity.intercept.method.aspectj.AspectJSecurityInterceptor">
      <property name="validateConfigAttributes"><value>true</value></property>
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="afterInvocationManager"><ref bean="afterInvocationManager"/></property>
      <property name="objectDefinitionSource">
        <value>
          org.acegisecurity.context.BankManager.delete*=ROLE_SUPERVISOR,RUN_AS_SERVER
          org.acegisecurity.context.BankManager.getBalance=ROLE_TELLER,ROLE_SUPERVISOR,BANKSECURITY_CUSTOMER,RUN_AS_SERVER
        </value>
      </property>
    </bean>

As you can see, aside from the class name, the `AspectJSecurityInterceptor` is exactly the same as the AOP Alliance security interceptor. Indeed the two interceptors can share the same `objectDefinitionSource`, as the `ObjectDefinitionSource` works with `java.lang.reflect.Method`s rather than an AOP library-specific class. Of course, your access decisions have access to the relevant AOP library-specific invocation (ie `MethodInvocation` or `JoinPoint`) and as such can consider a range of addition criteria when making access decisions (such as method arguments).

Next you'll need to define an AspectJ `aspect`. For example:

    package org.acegisecurity.samples.aspectj;

    import org.acegisecurity.intercept.method.aspectj.AspectJSecurityInterceptor;
    import org.acegisecurity.intercept.method.aspectj.AspectJCallback;
    import org.springframework.beans.factory.InitializingBean;

    public aspect DomainObjectInstanceSecurityAspect implements InitializingBean {

      private AspectJSecurityInterceptor securityInterceptor;

      pointcut domainObjectInstanceExecution(): target(PersistableEntity)
                 && execution(public * *(..)) && !within(DomainObjectInstanceSecurityAspect);

      Object around(): domainObjectInstanceExecution() {
        if (this.securityInterceptor != null) {
          AspectJCallback callback = new AspectJCallback() {
            public Object proceedWithObject() {
            return proceed();
          }
        };
        return this.securityInterceptor.invoke(thisJoinPoint, callback);
        } else {
          return proceed();
        }
      }

      public AspectJSecurityInterceptor getSecurityInterceptor() {
        return securityInterceptor;
      }

      public void setSecurityInterceptor(AspectJSecurityInterceptor securityInterceptor) {
        this.securityInterceptor = securityInterceptor;
      }

      public void afterPropertiesSet() throws Exception {
        if (this.securityInterceptor == null)
          throw new IllegalArgumentException("securityInterceptor required");
      }
    }

In the above example, the security interceptor will be applied to every instance of `PersistableEntity`, which is an abstract class not shown (you can use any other class or `pointcut` expression you like). For those curious, `AspectJCallback` is needed because the `proceed();` statement has special meaning only within an `around()` body. The `AspectJSecurityInterceptor` calls this anonymous `AspectJCallback` class when it wants the target object to continue.

You will need to configure Spring to load the aspect and wire it with the `AspectJSecurityInterceptor`. A bean declaration which achieves this is shown below:

    <bean id="domainObjectInstanceSecurityAspect"
        class="org.acegisecurity.samples.aspectj.DomainObjectInstanceSecurityAspect"
        factory-method="aspectOf">
      <property name="securityInterceptor"><ref bean="aspectJSecurityInterceptor"/></property>
    </bean>

That's it! Now you can create your beans from anywhere within your application, using whatever means you think fit (eg `new Person();`) and they will have the security interceptor applied.

### 1.5.4. FilterInvocation Security Interceptor

To secure `FilterInvocation`s, developers need to add a filter to their `web.xml` that delegates to the `SecurityEnforcementFilter`. A typical configuration example is provided below:

    <filter>
      <filter-name>Acegi HTTP Request Security Filter</filter-name>
      <filter-class>org.acegisecurity.util.FilterToBeanProxy</filter-class>
      <init-param>
        <param-name>targetClass</param-name>
        <param-value>org.acegisecurity.intercept.web.SecurityEnforcementFilter</param-value>
      </init-param>
    </filter>

    <filter-mapping>
      <filter-name>Acegi HTTP Request Security Filter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

Notice that the filter is actually a `FilterToBeanProxy`. Most of the filters used by the Acegi Security System for Spring use this class. Refer to the Filters section to learn more about this bean.

In the application context you will need to configure three beans:

    <bean id="securityEnforcementFilter" class="org.acegisecurity.intercept.web.SecurityEnforcementFilter">
      <property name="filterSecurityInterceptor"><ref bean="filterInvocationInterceptor"/></property>
      <property name="authenticationEntryPoint"><ref bean="authenticationEntryPoint"/></property>
    </bean>

    <bean id="authenticationEntryPoint" class="org.acegisecurity.ui.webapp.AuthenticationProcessingFilterEntryPoint">
      <property name="loginFormUrl"><value>/acegilogin.jsp</value></property>
      <property name="forceHttps"><value>false</value></property>
    </bean>

    <bean id="filterInvocationInterceptor" class="org.acegisecurity.intercept.web.FilterSecurityInterceptor">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="objectDefinitionSource">
        <value>
          CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
          \A/secure/super/.*\Z=ROLE_WE_DONT_HAVE
          \A/secure/.*\Z=ROLE_SUPERVISOR,ROLE_TELLER
        </value>
      </property>
    </bean>

The `AuthenticationEntryPoint` will be called if the user requests a secure HTTP resource but they are not authenticated. The class handles presenting the appropriate response to the user so that authentication can begin. Three concrete implementations are provided with the Acegi Security System for Spring: `AuthenticationProcessingFilterEntryPoint` for commencing a form-based authentication, `BasicProcessingFilterEntryPoint` for commencing a HTTP Basic authentication process, and `CasProcessingFilterEntryPoint` for commencing a Yale Central Authentication Service (CAS) login. The `AuthenticationProcessingFilterEntryPoint` and `CasProcessingFilterEntryPoint` have optional properties related to forcing the use of HTTPS, so please refer to the JavaDocs if you require this.

The `PortMapper` provides information on which HTTPS ports correspond to which HTTP ports. This is used by the `AuthenticationProcessingFilterEntryPoint` and several other beans. The default implementation, `PortMapperImpl`, knows the common HTTP ports 80 and 8080 map to HTTPS ports 443 and 8443 respectively. You can customise this mapping if desired.

The `SecurityEnforcementFilter` primarily provides session management support and initiates authentication when required. It delegates actual `FilterInvocation` security decisions to the configured `FilterSecurityInterceptor`.

Like any other security interceptor, the `FilterSecurityInterceptor` requires a reference to an `AuthenticationManager`, `AccessDecisionManager` and `RunAsManager`, which are each discussed in separate sections below. The `FilterSecurityInterceptor` is also configured with configuration attributes that apply to different HTTP URL requests. A full discussion of configuration attributes is provided in the High Level Design section of this document.

The `FilterSecurityInterceptor` can be configured with configuration attributes in two ways. The first is via a property editor and the application context, which is shown above. The second is via writing your own `ObjectDefinitionSource`, although this is beyond the scope of this document. Irrespective of the approach used, the `ObjectDefinitionSource` is responsible for returning a `ConfigAttributeDefinition` object that contains all of the configuration attributes associated with a single secure HTTP URL.

It should be noted that the `FilterSecurityInterceptor.setObjectDefinitionSource()` method actually expects an instance of `FilterInvocationDefinitionSource`. This is a marker interface which subclasses `ObjectDefinitionSource`. It simply denotes the `ObjectDefinitionSource` understands `FilterInvocation`s. In the interests of simplicity we'll continue to refer to the `FilterInvocationDefinitionSource` as an `ObjectDefinitionSource`, as the distinction is of little relevance to most users of the `FilterSecurityInterceptor`.

If using the application context property editor approach (as shown above), commas are used to delimit the different configuration attributes that apply to each HTTP URL. Each configuration attribute is assigned into its own `SecurityConfig` object. The `SecurityConfig` object is discussed in the High Level Design section. The `ObjectDefinitionSource` created by the property editor, `FilterInvocationDefinitionSource`, matches configuration attributes against `FilterInvocations` based on expression evaluation of the request URL. Two standard expression syntaxes are supported. The default is to treat all expressions as regular expressions. Alternatively, the presence of a `PATTERN_TYPE_APACHE_ANT` directive will cause all expressions to be treated as Apache Ant paths. It is not possible to mix expression syntaxes within the same definition. For example, the earlier configuration could be generated using Apache Ant paths as follows:

    <bean id="filterInvocationInterceptor" class="org.acegisecurity.intercept.web.FilterSecurityInterceptor">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref bean="accessDecisionManager"/></property>
      <property name="runAsManager"><ref bean="runAsManager"/></property>
      <property name="objectDefinitionSource">
        <value>
          CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
          PATTERN_TYPE_APACHE_ANT
          /secure/super/**=ROLE_WE_DONT_HAVE
          /secure/**=ROLE_SUPERVISOR,ROLE_TELLER
        </value>
      </property>
    </bean>

Irrespective of the type of expression syntax used, expressions are always evaluated in the order they are defined. Thus it is important that more specific expressions are defined higher in the list than less specific expressions. This is reflected in our example above, where the more specific `/secure/super/` pattern appears higher than the less specific `/secure/` pattern. If they were reversed, the `/secure/` pattern would always match and the `/secure/super/` pattern would never be evaluated.

The special keyword `CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON` causes the `FilterInvocationDefinitionSource` to automatically convert a request URL to lowercase before comparison against the expressions. Whilst by default the case of the request URL is not converted, it is generally recommended to use `CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON` and write each expression assuming lowercase.

As with other security interceptors, the `validateConfigAttributes` property is observed. When set to `true` (the default), at startup time the `FilterSecurityInterceptor` will evaluate if the provided configuration attributes are valid. It does this by checking each configuration attribute can be processed by either the `AccessDecisionManager` or the `RunAsManager`. If neither of these can process a given configuration attribute, an exception is thrown.

## 1.6. Authentication

### 1.6.1. Authentication Requests

Authentication requires a way for client code to present its security identification to the Acegi Security System for Spring. This is the role of the `Authentication` interface. The `Authentication` interface holds three important objects: the principal (the identity of the caller), the credentials (the proof of the identity of the caller, such as a password), and the authorities that have been granted to the principal. The principal and its credentials are populated by the client code, whilst the granted authorities are populated by the `AuthenticationManager`.

Figure 3: Key Authentication Architecture

As shown in Figure 3, the Acegi Security System for Spring includes several concrete `Authentication` implementations:

- `UsernamePasswordAuthenticationToken` allows a username and password to be presented as the principal and credentials respectively. It is also what is created by the HTTP Session Authentication system.

- `TestingAuthenticationToken` facilitates unit testing by automatically being considered an authenticated object by its associated `AuthenticationProvider`.

- `RunAsUserToken` is used by the default run-as authentication replacement implementation. This is discussed further in the Run-As Authentication Replacement section.

- `CasAuthenticationToken` is used to represent a successful Yale Central Authentication Service (CAS) authentication. This is discussed further in the CAS section.

- `PrincipalAcegiUserToken` and `JettyAcegiUserToken` implement `AuthByAdapter` (a subclass of `Authentication`) and are used whenever authentication is completed by Acegi Security System for Spring container adapters. This is discussed further in the Container Adapters section.

The authorities granted to a principal are represented by the `GrantedAuthority` interface. The `GrantedAuthority` interface is discussed at length in the Authorization section.

### 1.6.2. Authentication Manager

As discussed in the Security Interception section, the `AbstractSecurityInterceptor` extracts the `Authentication` object from the `SecurityContext` in the `SecurityContextHolder`. This is then passed to an `AuthenticationManager`. The `AuthenticationManager` interface is very simple:

    public Authentication authenticate(Authentication authentication) throws AuthenticationException;

Implementations of `AuthenticationManager` are required to throw an `AuthenticationException` should authentication fail, or return a fully populated `Authentication` object. In particular, the returned `Authentication` object should contain an array of `GrantedAuthority` objects. The `SecurityInterceptor` places the populated `Authentication` object back in the `SecurityContext` in the `SecurityContextHolder`, overwriting the original `Authentication` object.

The `AuthenticationException` has a number of subclasses. The most important are `BadCredentialsException` (an incorrect principal or credentials), `DisabledException` and `LockedException`. The latter two exceptions indicate the principal was found, but the credentials were not checked and authentication is denied. An `AuthenticationServiceException` is also provided, which indicates the authentication system could not process the request (eg a database was unavailable). `AuthenticationException` also has a `CredentialsExpiredException` and `AccoungtExpiredException` subclass, although these are less commonly used.

### 1.6.3. Provider-Based Authentication

Whilst the basic `Authentication` and `AuthenticationManager` interfaces enable users to develop their own authentication systems, users should consider using the provider-based authentication packages provided by the Acegi Security System for Spring. The key class, `ProviderManager`, is configured via the bean context with a list of `AuthenticationProvider`s:

    <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
      <property name="providers">
        <list>
          <ref bean="daoAuthenticationProvider"/>
          <ref bean="someOtherAuthenticationProvider"/>
        </list>
      </property>
    </bean>

`ProviderManager` calls a series of registered `AuthenticationProvider` implementations, until one is found that indicates it is able to authenticate a given `Authentication` class. When the first compatible `AuthenticationProvider` is located, it is passed the authentication request. The `AuthenticationProvider` will then either throw an `AuthenticationException` or return a fully populated `Authentication` object.

Note the `ProviderManager` may throw a `ProviderNotFoundException` (a subclass of `AuthenticationException`) if it none of the registered `AuthenticationProviders` can validate the `Authentication` object.

The `ProviderManager` also has several other important functions. It integrates with concurrent session handling supoprt, and it also converts any exceptions thrown by an `AuthenticationProvider` and publishes a suitable event. The events that are published are located in the `org.acegisecurity.event.authentication` package and advanced users can map different exceptions to different events by configuring the `ProviderManager.exceptionMappings` property (generally this is not required and the default event propagation is appropriate - especially as events will simply be ignored if you don't have an `ApplicationListener` configured in the `ApplicationContext`).

Several `AuthenticationProvider` implementations are provided with the Acegi Security System for Spring:

- `TestingAuthenticationProvider` is able to authenticate a `TestingAuthenticationToken`. The limit of its authentication is simply to treat whatever is contained in the `TestingAuthenticationToken` as valid. This makes it ideal for use during unit testing, as you can create an `Authentication` object with precisely the `GrantedAuthority` objects required for calling a given method. You definitely would not register this `AuthenticationProvider` on a production system.

- `DaoAuthenticationProvider` is able to authenticate a `UsernamePasswordAuthenticationToken` by accessing an authentication respository via a data access object. This is discussed further below, as it is the main way authentication is initially handled.

- `RunAsImplAuthenticationProvider` is able to authenticate a `RunAsUserToken`. This is discussed further in the Run-As Authentication Replacement section. You would not register this `AuthenticationProvider` if you were not using run-as replacement.

- `AuthByAdapterProvider` is able to authenticate any `AuthByAdapter` (a subclass of `Authentication` used with container adapters). This is discussed further in the Container Adapters section. You would not register this `AuthenticationProvider` if you were not using container adapters.

- `CasAuthenticationProvider` is able to authenticate Yale Central Authentication Service (CAS) tickets. This is discussed further in the CAS Single Sign On section.

- `JaasAuthenticationProvider` is able to delegate authentication requests to a JAAS `LoginModule`. This is discussed further below.

### 1.6.4. Concurrent Session Support

Acegi Security is able to stop the same principal authenticating to the same web application multiple times concurrently. Put differently, you can stop user "Batman" from logging into a web application twice at the same time.

To use concurrent session support, you'll need to add the following to web.xml:

    <listener>
      <listener-class>org.acegisecurity.ui.session.HttpSessionEventPublisher</listener-class>
    </listener>

In addition, you will need to add the `org.acegisecurity.concurrent.ConcurrentSessionFilter` to your `FilterChainProxy`. The ConcurrentSessionFilter requires only one property, sessionRegistry, which generally points to an instance of `SessionRegistryImpl`.

The `web.xml` `HttpSessionEventPublisher` causes an `ApplicationEvent` to be published to the Spring `ApplicationContext` every time a `HttpSession` commences or terminates. This is critical, as it allows the `SessionRegistryImpl` to be notified when a session ends.

You will also need to wire up the `ConcurrentSessionControllerImpl` and refer to it from your `ProviderManager` bean:

    <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
      <property name="providers">
        <!-- your providers go here -->
      </property>
      <property name="sessionController"><ref bean="concurrentSessionController"/></property>
    </bean>

    <bean id="concurrentSessionController" class="org.acegisecurity.concurrent.ConcurrentSessionControllerImpl">
      <property name="maximumSessions"><value>1</value></property>
      <property name="sessionRegistry"><ref local="sessionRegistry"/></property>
    </bean>

    <bean id="sessionRegistry" class="org.acegisecurity.concurrent.SessionRegistryImpl"/>

### 1.6.5. Data Access Object Authentication Provider

The Acegi Security System for Spring includes a production-quality `AuthenticationProvider` implementation called `DaoAuthenticationProvider`. This authentication provider is able to authenticate a `UsernamePasswordAuthenticationToken` by obtaining authentication details from a data access object configured at bean creation time:

    <bean id="daoAuthenticationProvider" class="org.acegisecurity.providers.dao.DaoAuthenticationProvider">
      <property name="userDetailsService"><ref bean="inMemoryDaoImpl"/></property>
      <property name="saltSource"><ref bean="saltSource"/></property>
      <property name="passwordEncoder"><ref bean="passwordEncoder"/></property>
    </bean>

The `PasswordEncoder` and `SaltSource` are optional. A `PasswordEncoder` provides encoding and decoding of passwords obtained from the authentication repository. A `SaltSource` enables the passwords to be populated with a "salt", which enhances the security of the passwords in the authentication repository. `PasswordEncoder` implementations are provided with the Acegi Security System for Spring covering MD5, SHA and cleartext encodings. Two `SaltSource` implementations are also provided: `SystemWideSaltSource` which encodes all passwords with the same salt, and `ReflectionSaltSource`, which inspects a given property of the returned `UserDetails` object to obtain the salt. Please refer to the JavaDocs for further details on these optional features.

In addition to the properties above, the `DaoAuthenticationProvider` supports optional caching of `UserDetails` objects. The `UserCache` interface enables the `DaoAuthenticationProvider` to place a `UserDetails` object into the cache, and retrieve it from the cache upon subsequent authentication attempts for the same username. By default the `DaoAuthenticationProvider` uses the `NullUserCache`, which performs no caching. A usable caching implementation is also provided, `EhCacheBasedUserCache`, which is configured as follows:

    <bean id="daoAuthenticationProvider" class="org.acegisecurity.providers.dao.DaoAuthenticationProvider">
      <property name="userDetailsService"><ref bean="userDetailsService"/></property>
      <property name="userCache"><ref bean="userCache"/></property>
    </bean>

    <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean">
      <property name="configLocation">
        <value>classpath:/ehcache-failsafe.xml</value>
      </property>
    </bean>

    <bean id="userCacheBackend" class="org.springframework.cache.ehcache.EhCacheFactoryBean">
      <property name="cacheManager">
        <ref local="cacheManager"/>
      </property>
      <property name="cacheName">
        <value>userCache</value>
      </property>
    </bean>

    <bean id="userCache" class="org.acegisecurity.providers.dao.cache.EhCacheBasedUserCache">
      <property name="cache"><ref local="userCacheBackend"/></property>
    </bean>

All Acegi Security EH-CACHE implementations (including `EhCacheBasedUserCache`) require an EH-CACHE `Cache` object. The `Cache` object can be obtained from wherever you like, although we recommend you use Spring's factory classes as shown in the above configuration. If using Spring's factory classes, please refer to the Spring documentation for further details on how to optimise the cache storage location, memory usage, eviction policies, timeouts etc.

For a class to be able to provide the `DaoAuthenticationProvider` with access to an authentication repository, it must implement the `UserDetailsService` interface:

    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException, DataAccessException;

The `UserDetails` is an interface that provides getters that guarantee non-null provision of basic authentication information such as the username, password, granted authorities and whether the user is enabled or disabled. A concrete implementation, `User`, is also provided. Acegi Security users will need to decide when writing their `UserDetailsService` what type of `UserDetails` to return. In most cases `User` will be used directly or subclassed, although special circumstances (such as object relational mappers) may require users to write their own `UserDetails` implementation from scratch. `UserDetails` is often used to store additional principal-related properties (such as their telephone number and email address), so they can be easily used by web views.

Given `UserDetailsService` is so simple to implement, it should be easy for users to retrieve authentication information using a persistence strategy of their choice.

A design decision was made not to support account locking in the `DaoAuthenticationProvider`, as doing so would have increased the complexity of the `UserDetailsService` interface. For instance, a method would be required to increase the count of unsuccessful authentication attempts. Such functionality could be easily provided by leveraging the application event publishing features discussed below.

`DaoAuthenticationProvider` returns an `Authentication` object which in turn has its `principal` property set. The principal will be either a `String` (which is essentially the username) or a `UserDetails` object (which was looked up from the `UserDetailsService`). By default the `UserDetails` is returned, as this enables applications to add extra properties potentially of use in applications, such as the user's full name, email address etc. If using container adapters, or if your applications were written to operate with `String`s (as was the case for releases prior to Acegi Security 0.6), you should set the `DaoAuthenticationProvider.forcePrincipalAsString` property to `true` in your application context.

### 1.6.6. In-Memory Authentication

Whilst it is easy to use the `DaoAuthenticationProvider` and create a custom `UserDetailsService` implementation that extracts information from a persistence engine of choice, many applications do not require such complexity. One alternative is to configure an authentication repository in the application context itself using the `InMemoryDaoImpl`:

    <bean id="inMemoryDaoImpl" class="org.acegisecurity.userdetails.memory.InMemoryDaoImpl">
      <property name="userMap">
        <value>
          marissa=koala,ROLE_TELLER,ROLE_SUPERVISOR
          dianne=emu,ROLE_TELLER
          scott=wombat,ROLE_TELLER
          peter=opal,disabled,ROLE_TELLER
        </value>
      </property>
    </bean>

The `userMap` property contains each of the usernames, passwords, a list of granted authorities and an optional enabled/disabled keyword. Commas delimit each token. The username must appear to the left of the equals sign, and the password must be the first token to the right of the equals sign. The `enabled` and `disabled` keywords (case insensitive) may appear in the second or any subsequent token. Any remaining tokens are treated as granted authorities, which are created as `GrantedAuthorityImpl` objects (refer to the Authorization section for further discussion on granted authorities). Note that if a user has no password and/or no granted authorities, the user will not be created in the in-memory authentication repository.

`InMemoryDaoImpl` also offers a `setUserProperties(Properties)` method, which allows you to externalise the `java.util.Properties` in another Spring configured bean or an external properties file. This might prove useful for simple applications that have a larger number of users, or deployment-time configuration changes, but do not wish to use a full database for authentication details.

### 1.6.7. JDBC Authentication

The Acegi Security System for Spring also includes an authentication provider that can obtain authentication information from a JDBC data source. The typical configuration for the `JdbcDaoImpl` is shown below:

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
      <property name="driverClassName"><value>org.hsqldb.jdbcDriver</value></property>
      <property name="url"><value>jdbc:hsqldb:hsql://localhost:9001</value></property>
      <property name="username"><value>sa</value></property>
      <property name="password"><value></value></property>
    </bean>

    <bean id="jdbcDaoImpl" class="org.acegisecurity.userdetails.jdbc.JdbcDaoImpl">
      <property name="dataSource"><ref bean="dataSource"/></property>
    </bean>

You can use different relational database management systems by modifying the `DriverManagerDataSource` shown above. Irrespective of the database used, a standard schema must be used as indicated in `dbinit.txt`.

If you default schema is unsuitable for your needs, `JdbcDaoImpl` provides two properties that allow customisation of the SQL statements. You may also subclass the `JdbcDaoImpl` if further customisation is necessary. Please refer to the JavaDocs for details.

### 1.6.8. JAAS Authentication

Acegi Security provides a package able to delegate authentication requests to the Java Authentication and Authorization Service (JAAS). This package is discussed in detail below.

Central to JAAS operation are login configuration files. To learn more about JAAS login configuration files, consult the JAAS reference documentation available from Sun Microsystems. We expect you to have a basic understanding of JAAS and its login configuration file syntax in order to understand this section.

#### 1.6.8.1. JaasAuthenticationProvider

The `JaasAuthenticationProvider` attempts to authenticate a user’s principal and credentials through JAAS.

Let’s assume we have a JAAS login configuration file, `/WEB-INF/login.conf`, with the following contents:

    JAASTest {
      sample.SampleLoginModule required;
    };

Like all Acegi Security beans, the `JaasAuthenticationProvider` is configured via the application context. The following definitions would correspond to the above JAAS login configuration file:

    <bean id="jaasAuthenticationProvider" class="org.acegisecurity.providers.jaas.JaasAuthenticationProvider">
      <property name="loginConfig">
        <value>/WEB-INF/login.conf</value>
      </property>
      <property name="loginContextName">
        <value>JAASTest</value>
      </property>
      <property name="callbackHandlers">
        <list>
          <bean class="org.acegisecurity.providers.jaas.JaasNameCallbackHandler"/>
          <bean class="org.acegisecurity.providers.jaas.JaasPasswordCallbackHandler"/>
        </list>
      </property>
      <property name="authorityGranters">
        <list>
          <bean class="org.acegisecurity.providers.jaas.TestAuthorityGranter"/>
        </list>
      </property>
    </bean>

The `CallbackHandler`s and `AuthorityGranter`s are discussed below.

#### 1.6.8.2. Callbacks

Most JAAS `LoginModule`s require a callback of some sort. These callbacks are usually used to obtain the username and password from the user. In an Acegi Security deployment, Acegi Security is responsible for this user interaction (typically via a reference to a `ContextHolder`-managed `Authentication` object). The JAAS package for Acegi Security provides two default callback handlers, `JaasNameCallbackHandler` and `JaasPasswordCallbackHandler`. Each of these callback handlers implement `JaasAuthenticationCallbackHandler`. In most cases these callback handlers can simply be used without understanding the internal mechanics. For those needing full control over the callback behavior, internally `JaasAutheticationProvider` wraps these `JaasAuthenticationCallbackHandler`s with an `InternalCallbackHandler`. The `InternalCallbackHandler` is the class that actually implements JAAS’ normal `CallbackHandler` interface. Any time that the JAAS `LoginModule` is used, it is passed a list of application context configured `InternalCallbackHandler`s. If the `LoginModule` requests a callback against the `InternalCallbackHandler`s, the callback is in-turn passed to the `JaasAuthenticationCallbackHandler`s being wrapped.

#### 1.6.8.3. AuthorityGranters

JAAS works with principals. Even “roles” are represented as principals in JAAS. Acegi Security, on the other hand, works with `Authentication` objects. Each `Authentication` object contains a single principal, and multiple `GrantedAuthority`[]s. To facilitate mapping between these different concepts, the Acegi Security JAAS package includes an `AuthorityGranter` interface. An `AuthorityGranter` is responsible for inspecting a JAAS principal and returning a `String`. The `JaasAuthenticationProvider` then creates a `JaasGrantedAuthority` (which implements Acegi Security’s `GrantedAuthority` interface) containing both the `AuthorityGranter`-returned `String` and the JAAS principal that the `AuthorityGranter` was passed. The `JaasAuthenticationProvider` obtains the JAAS principals by firstly successfully authenticating the user’s credentials using the JAAS `LoginModule`, and then accessing the `LoginContext` it returns. A call to `LoginContext.getSubject().getPrincipals()` is made, with each resulting principal passed to each `AuthorityGranter` defined against the `JaasAuthenticationProvider.setAuthorityGranters(List)` property. Acegi Security does not include any production `AuthorityGranter`s given every JAAS principal has an implementation-specific meaning. However, there is a `TestAuthorityGranter` in the unit tests that demonstrates a simple `AuthorityGranter` implementation.

### 1.6.9. Siteminder Authentication

Acegi Security provides a web filter `(org.acegisecurity.ui.webapp.SiteminderAuthenticationProcessingFilter`) that can be used to process requests that have been pre-authenticated by Computer Associates' Siteminder. This filter assumes that you're using Siteminder for authentication, and your application (or backing datasource) is used for authorization. The use of Siteminder for authorization is not yet directly supported by Acegi.

Recall that a Siteminder agent is set up on your web server to intercept a user's first call to your application. This agent redirects the initial request to a login page, and only after successful authentication does your application receive the request. Authenticated requests contain one or more HTTP headers populated by the Siteminder agent. Below we'll assume that the request header key containing the user's identity is "SM_USER", but of course your header values may be different based on Siteminder policy server configuration. Please refer to your company's "single sign-on" group for header details.

#### 1.6.9.1. SiteminderAuthenticationProcessingFilter

The first step in setting up Acegi's Siteminder support is to define an `authenticationProcessingFilter` bean and give it an `authenticationManager` to use, as well as to tell it where to send users upon success and failure and where to find the Siteminder username and password values. Most people won't need the password value since Siteminder has already authenticated the user, so it's typical to use the same header for both.

       <!-- ======================== SITEMINDER AUTHENTICATION PROCESSING FILTER ======================= -->
       <bean id="authenticationProcessingFilter" class="org.acegisecurity.ui.webapp.SiteminderAuthenticationProcessingFilter">
          <property name="authenticationManager"><ref bean="authenticationManager"/></property>
          <property name="authenticationFailureUrl"><value>/login.jsp?login_error=1</value></property>
          <property name="defaultTargetUrl"><value>/security.do?method=getMainMenu</value></property>
          <property name="filterProcessesUrl"><value>/j_acegi_security_check</value></property>
          <property name="siteminderUsernameHeaderKey"><value>SM_USER</value></property>
          <property name="siteminderPasswordHeaderKey"><value>SM_USER</value></property>
       </bean>

Since this `authenticationProcessingFilter` depends on an `authenticationManager`, we'll need to define one:

        <!-- ======================== AUTHENTICATION ======================= -->
        <!--
          - The top-level Authentication Manager is responsible for all application AUTHENTICATION
          - operations.  Note that it must reference one or more provider(s) defined below.
          -->
        <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
            <property name="providers">
                <list>
                    <ref local="daoAuthenticationProvider"/>
                </list>
            </property>
        </bean>

Note that your `daoAuthenticationProvider` above will expect the password property to match what it expects. In this case, authentication has already been handled by Siteminder and you've specified the same HTTP header for both username and password, so you can code `daoAuthenticationProvider` to simply make sure the username and password values match. This may sound like a security weakness, but remember that users have to authenticate with Siteminder before your application ever receives the requests, so the purpose of your `daoAuthenticationProvider` should simply be to assign roles and other properties needed by subsequent method interceptors, etc.

Finally we need to tell the `filterChainProxy` to include the `authenticationProcessingFilter` in its operations.

        <!-- ======================== FILTER CHAIN ======================= -->
        <!--
          - The web.xml file has a single filter reference to this top-level bean, which
          - invokes the chain of sub-filters specified below.
          -->
        <bean id="filterChainProxy" class="org.acegisecurity.util.FilterChainProxy">
          <property name="filterInvocationDefinitionSource">
             <value>
                 CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
                 PATTERN_TYPE_APACHE_ANT
                /**=httpSessionContextIntegrationFilter,authenticationProcessingFilter,securityEnforcementFilter
             </value>
          </property>
        </bean>

In summary, once the user has authenticated through Siteminder, their header-loaded request will be brokered by `filterChainProxy` to `authenticationProcessingFilter`, which in turn will grab the user's identity from the SM_USER request header. The user's identity will then be passed to the `authenticationManager` and finally `daoAuthenticationProvider` will do the work of authorizing the user against back-end databases, etc. and loading the `UserDetails` implementation with roles, username and any other property you deem relevant.

### 1.6.10. Authentication Recommendations

With the heavy use of interfaces throughout the authentication system (`Authentication`, `AuthenticationManager`, `AuthenticationProvider` and `UserDetailsService`) it might be confusing to a new user to know which part of the authentication system to customize. In general, the following is recommended:

- Use the `UsernamePasswordAuthenticationToken` implementation where possible.

- If you simply need to implement a new authentication repository (eg to obtain user details from your application’s existing database), use the `DaoAuthenticationProvider` along with the `UserDetailsService`. It is the fastest and safest way to integrate an external database.

- If you're using Container Adapters or a `RunAsManager` that replaces the `Authentication` object, ensure you have registered the `AuthByAdapterProvider` and `RunAsManagerImplProvider` respectively with your `ProviderManager`.

- Never enable the `TestingAuthenticationProvider` on a production system. Doing so will allow any client to simply present a `TestingAuthenticationToken` and obtain whatever access they request.

- Adding a new `AuthenticationProvider` is sufficient to support most custom authentication requirements. Only unusual requirements would require the `ProviderManager` to be replaced with a different `AuthenticationManager`.

## 1.7. Authorization

### 1.7.1. Granted Authorities

As briefly mentioned in the Authentication section, all `Authentication` implementations are required to store an array of `GrantedAuthority` objects. These represent the authorities that have been granted to the principal. The `GrantedAuthority` objects are inserted into the `Authentication` object by the `AuthenticationManager` and are later read by `AccessDecisionManager`s when making authorization decisions.

`GrantedAuthority` is an interface with only one method:

    public String getAuthority();

This method allows `AccessDecisionManager`s to obtain a precise `String` representation of the `GrantedAuthority`. By returning a representation as a `String`, a `GrantedAuthority` can be easily "read" by most `AccessDecisionManager`s. If a `GrantedAuthority` cannot be precisely represented as a `String`, the `GrantedAuthority` is considered "complex" and `getAuthority()` must return `null`.

An example of a "complex" `GrantedAuthority` would be an implementation that stores a list of operations and authority thresholds that apply to different customer account numbers. Representing this complex `GrantedAuthority` as a `String` would be quite complex, and as a result the `getAuthority()` method should return `null`. This will indicate to any `AccessDecisionManager` that it will need to specifically support the `GrantedAuthority` implementation in order to understand its contents.

The Acegi Security System for Spring includes one concrete `GrantedAuthority` implementation, `GrantedAuthorityImpl`. This allows any user-specified `String` to be converted into a `GrantedAuthority`. All `AuthenticationProvider`s included with the security architecture use `GrantedAuthorityImpl` to populate the `Authentication` object.

### 1.7.2. Access Decision Managers

The `AccessDecisionManager` is called by the `AbstractSecurityInterceptor` and is responsible for making final access control decisions. The `AccessDecisionManager` interface contains three methods:

    public void decide(Authentication authentication, Object object, ConfigAttributeDefinition config) throws AccessDeniedException;
    public boolean supports(ConfigAttribute attribute);
    public boolean supports(Class clazz);

As can be seen from the first method, the `AccessDecisionManager` is passed via method parameters all information that is likely to be of value in assessing an authorization decision. In particular, passing the secure `Object` enables those arguments contained in the actual secure object invocation to be inspected. For example, let's assume the secure object was a `MethodInvocation`. It would be easy to query the `MethodInvocation` for any `Customer` argument, and then implement some sort of security logic in the `AccessDecisionManager` to ensure the principal is permitted to operate on that customer. Implementations are expected to throw an `AccessDeniedException` if access is denied.

The `supports(ConfigAttribute)` method is called by the `AbstractSecurityInterceptor` at startup time to determine if the `AccessDecisionManager` can process the passed `ConfigAttribute`. The `supports(Class)` method is called by a security interceptor implementation to ensure the configured `AccessDecisionManager` supports the type of secure object that the security interceptor will present.

### 1.7.3. Voting Decision Manager

Whilst users can implement their own `AccessDecisionManager` to control all aspects of authorization, the Acegi Security System for Spring includes several `AccessDecisionManager` implementations that are based on voting. Figure 4 illustrates the relevant classes.

Figure 4: Voting Decision Manager

Using this approach, a series of `AccessDecisionVoter` implementations are polled on an authorization decision. The `AccessDecisionManager` then decides whether or not to throw an `AccessDeniedException` based on its assessment of the votes.

The `AccessDecisionVoter` interface has three methods:

    public int vote(Authentication authentication, Object object, ConfigAttributeDefinition config);
    public boolean supports(ConfigAttribute attribute);
    public boolean supports(Class clazz);

Concrete implementations return an `int`, with possible values being reflected in the `AccessDecisionVoter` static fields `ACCESS_ABSTAIN`, `ACCESS_DENIED` and `ACCESS_GRANTED`. A voting implementation will return `ACCESS_ABSTAIN` if it has no opinion on an authorization decision. If it does have an opinion, it must return either `ACCESS_DENIED` or `ACCESS_GRANTED`.

There are three concrete `AccessDecisionManager`s provided with the Acegi Security System for Spring that tally the votes. The `ConsensusBased` implementation will grant or deny access based on the consensus of non-abstain votes. Properties are provided to control behavior in the event of an equality of votes or if all votes are abstain. The `AffirmativeBased` implementation will grant access if one or more `ACCESS_GRANTED` votes were received (ie a deny vote will be ignored, provided there was at least one grant vote). Like the `ConsensusBased` implementation, there is a parameter that controls the behavior if all voters abstain. The `UnanimousBased` provider expects unanimous `ACCESS_GRANTED` votes in order to grant access, ignoring abstains. It will deny access if there is any `ACCESS_DENIED` vote. Like the other implementations, there is a parameter that controls the behaviour if all voters abstain.

It is possible to implement a custom `AccessDecisionManager` that tallies votes differently. For example, votes from a particular `AccessDecisionVoter` might receive additional weighting, whilst a deny vote from a particular voter may have a veto effect.

There are two concrete `AccessDecisionVoter` implementations provided with the Acegi Security System for Spring. The `RoleVoter` class will vote if any ConfigAttribute begins with `ROLE_`. It will vote to grant access if there is a `GrantedAuthority` which returns a `String` representation (via the `getAuthority()` method) exactly equal to one or more `ConfigAttributes` starting with `ROLE_`. If there is no exact match of any `ConfigAttribute` starting with `ROLE_`, the `RoleVoter` will vote to deny access. If no `ConfigAttribute` begins with `ROLE_`, the voter will abstain. `RoleVoter` is case sensitive on comparisons as well as the `ROLE_` prefix.

BasicAclEntryVoter is the other concrete voter included with Acegi Security. It integrates with Acegi Security's `AclManager` (discussed later). This voter is designed to have multiple instances in the same application context, such as:

    <bean id="aclContactReadVoter" class="org.acegisecurity.vote.BasicAclEntryVoter">
      <property name="processConfigAttribute"><value>ACL_CONTACT_READ</value></property>
      <property name="processDomainObjectClass"><value>sample.contact.Contact</value></property>
      <property name="aclManager"><ref local="aclManager"/></property>
      <property name="requirePermission">
        <list>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.ADMINISTRATION"/>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.READ"/>
        </list>
      </property>
    </bean>

    <bean id="aclContactDeleteVoter" class="org.acegisecurity.vote.BasicAclEntryVoter">
      <property name="processConfigAttribute"><value>ACL_CONTACT_DELETE</value></property>
      <property name="processDomainObjectClass"><value>sample.contact.Contact</value></property>
      <property name="aclManager"><ref local="aclManager"/></property>
      <property name="requirePermission">
        <list>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.ADMINISTRATION"/>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.DELETE"/>
        </list>
      </property>
    </bean>

In the above example, you'd define `ACL_CONTACT_READ` or `ACL_CONTACT_DELETE` against some methods on a `MethodSecurityInterceptor` or `AspectJSecurityInterceptor`. When those methods are invoked, the above applicable voter defined above would vote to grant or deny access. The voter would look at the method invocation to locate the first argument of type `sample.contact.Contact`, and then pass that `Contact` to the `AclManager`. The `AclManager` will then return an access control list (ACL) that applies to the current `Authentication`. Assuming that ACL contains one of the listed `requirePermission`s, the voter will vote to grant access. If the ACL does not contain one of the permissions defined against the voter, the voter will vote to deny access. `BasicAclEntryVoter` is an important class as it allows you to build truly complex applications with domain object security entirely defined in the application context. If you're interested in learning more about Acegi Security's ACL capabilities and how best to apply them, please see the ACL and "After Invocation" sections of this reference guide, and the Contacts sample application.

It is also possible to implement a custom `AccessDecisionVoter`. Several examples are provided in the Acegi Security System for Spring unit tests, including `ContactSecurityVoter` and `DenyVoter`. The `ContactSecurityVoter` abstains from voting decisions where a `CONTACT_OWNED_BY_CURRENT_USER` `ConfigAttribute` is not found. If voting, it queries the `MethodInvocation` to extract the owner of the `Contact` object that is subject of the method call. It votes to grant access if the `Contact` owner matches the principal presented in the `Authentication` object. It could have just as easily compared the `Contact` owner with some `GrantedAuthority` the `Authentication` object presented. All of this is achieved with relatively few lines of code and demonstrates the flexibility of the authorization model.

### 1.7.4. Authorization-Related Tag Libraries

The Acegi Security System for Spring comes bundled with several JSP tag libraries that eases JSP writing. The tag libraries are known as `authz` and provide a range of different services.

All taglib classes are included in the core `acegi-security-xx.jar` file, with the `authz.tld` located in the JAR's `META-INF` directory. This means for JSP 1.2+ web containers you can simply include the JAR in the WAR's `WEB-INF/lib` directory and it will be available. If you're using a JSP 1.1 container, you'll need to declare the JSP taglib in your `web.xml file`, and include `authz.tld` in the `WEB-INF/lib` directory. The following fragment is added to `web.xml`:

    <taglib>
           <taglib-uri>http://acegisecurity.sf.net/authz</taglib-uri>
           <taglib-location>/WEB-INF/authz.tld</taglib-location>
    </taglib>

#### 1.7.4.1. AuthorizeTag

`AuthorizeTag` is used to include content if the current principal holds certain `GrantedAuthority`s.

The following JSP fragment illustrates how to use the `AuthorizeTag`:

    <authz:authorize ifAllGranted="ROLE_SUPERVISOR">
      <td>
        <A HREF="del.htm?id=<c:out value="${contact.id}"/>">Del</A>
      </td>
    </authz:authorize>

This tag would cause the tag's body to be output if the principal has been granted ROLE_SUPERVISOR.

The `authz:authorize` tag declares the following attributes:

- `ifAllGranted`: All the listed roles must be granted for the tag to output its body.

- `ifAnyGranted`: Any of the listed roles must be granted for the tag to output its body.

- `ifNotGranted`: None of the listed roles must be granted for the tag to output its body.

You'll note that in each attribute you can list multiple roles. Simply separate the roles using a comma. The `authorize` tag ignores whitespace in attributes.

The tag library logically ANDs all of it's parameters together. This means that if you combine two or more attributes, all attributes must be true for the tag to output it's body. Don't add an `ifAllGranted="ROLE_SUPERVISOR"`, followed by an `ifNotGranted="ROLE_SUPERVISOR"`, or you'll be surprised to never see the tag's body.

By requiring all attributes to return true, the authorize tag allows you to create more complex authorization scenarios. For example, you could declare an `ifAllGranted="ROLE_SUPERVISOR"` and an `ifNotGranted="ROLE_NEWBIE_SUPERVISOR"` in the same tag, in order to prevent new supervisors from seeing the tag body. However it would no doubt be simpler to use `ifAllGranted="ROLE_EXPERIENCED_SUPERVISOR"` rather than inserting NOT conditions into your design.

One last item: the tag verifies the authorizations in a specific order: first `ifNotGranted`, then `ifAllGranted`, and finally, `ifAnyGranted`.

#### 1.7.4.2. AuthenticationTag

`AuthenticationTag` is used to simply output a property of the current principal's `Authentication.getPrincipal()` object to the web page.

The following JSP fragment illustrates how to use the `AuthenticationTag`:

    <authz:authentication operation="username"/>

This tag would cause the principal's name to be output. Here we are assuming the `Authentication.getPrincipal()` is a `UserDetails` object, which is generally the case when using the typical `DaoAuthenticationProvider`.

#### 1.7.4.3. AclTag

`AclTag` is used to include content if the current principal has a ACL to the indicated domain object.

The following JSP fragment illustrates how to use the `AclTag`:

    <authz:acl domainObject="${contact}" hasPermission="16,1">
      <td><A HREF="<c:url value="del.htm"><c:param name="contactId" value="${contact.id}"/></c:url>">Del</A></td>
    </authz:acl>

This tag would cause the tag's body to be output if the principal holds either permission 16 or permission 1 for the "contact" domain object. The numbers are actually integers that are used with `AbstractBasicAclEntry` bit masking. Please refer tro the ACL section of this reference guide to understand more about the ACL capabilities of Acegi Security.

### 1.7.5. Authorization Recommendations

Given there are several ways to achieve similar authorization outcomes in the Acegi Security System for Spring, the following general recommendations are made:

- Grant authorities using `GrantedAuthorityImpl` where possible. Because it is already supported by the Acegi Security System for Spring, you avoid the need to create custom `AuthenticationManager` or `AuthenticationProvider` implementations simply to populate the `Authentication` object with a custom `GrantedAuthority`.

- Writing an `AccessDecisionVoter` implementation and using either `ConsensusBased`, `AffirmativeBased` or `UnanimousBased` as the `AccessDecisionManager` may be the best approach to implementing your custom access decision rules.

## 1.8. After Invocation Handling

### 1.8.1. Overview

Whilst the `AccessDecisionManager` is called by the `AbstractSecurityInterceptor` before proceeding with the secure object invocation, some applications need a way of modifying the object actually returned by the secure object invocation. Whilst you could easily implement your own AOP concern to achieve this, Acegi Security provides a convenient hook that has several concrete implementations that integrate with its ACL capabilities.

Figure 5 illustrates Acegi Security's `AfterInvocationManager` and its concrete implementations.

Figure 5: After Invocation Implementation

Like many other parts of Acegi Security, `AfterInvocationManager` has a single concrete implementation, `AfterInvocationProvider`, which polls a list of `AfterInvocationProvider`s. Each `AfterInvocationProvider` is allowed to modify the return object or throw an `AccessDeniedException`. Indeed multiple providers can modify the object, as the result of the previous provider is passed to the next in the list. Let's now consider our ACL-aware implementations of `AfterInvocationProvider`.

Please be aware that if you're using `AfterInvocationManager`, you will still need configuration attributes that allow the `MethodSecurityInterceptor`'s `AccessDecisionManager` to allow an operation. If you're using the typical Acegi Security included `AccessDecisionManager` implementations, having no configuration attributes defined for a particular secure method invocation will cause each `AccessDecisionVoter` to abstain from voting. In turn, if the `AccessDecisionManager` property "`allowIfAllAbstainDecisions`" is `false`, an `AccessDeniedException` will be thrown. You may avoid this potential issue by either (i) setting "`allowIfAllAbstainDecisions`" to `true` (although this is generally not recommended) or (ii) simply ensure that there is at least one configuration attribute that an `AccessDecisionVoter` will vote to grant access for. This latter (recommended) approach is usually achieved through a `ROLE_USER` or `ROLE_AUTHENTICATED` configuration attribute.

### 1.8.2. ACL-Aware AfterInvocationProviders

A common services layer method we've all written at one stage or another looks like this:

    public Contact getById(Integer id);

Quite often, only principals with permission to read the `Contact` should be allowed to obtain it. In this situation the `AccessDecisionManager` approach provided by the `AbstractSecurityInterceptor` will not suffice. This is because the identity of the `Contact` is all that is available before the secure object is invoked. The `BasicAclAfterInvocationProvider` delivers a solution, and is configured as follows:

    <bean id="afterAclRead" class="org.acegisecurity.afterinvocation.BasicAclEntryAfterInvocationProvider">
      <property name="aclManager"><ref local="aclManager"/></property>
      <property name="requirePermission">
        <list>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.ADMINISTRATION"/>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.READ"/>
        </list>
      </property>
    </bean>

In the above example, the `Contact` will be retrieved and passed to the `BasicAclEntryAfterInvocationProvider`. The provider will thrown an `AccessDeniedException` if one of the listed `requirePermission`s is not held by the `Authentication`. The `BasicAclEntryAfterInvocationProvider` queries the `AclManager` to determine the ACL that applies for this domain object to this `Authentication`.

Similar to the `BasicAclEntryAfterInvocationProvider` is `BasicAclEntryAfterInvocationCollectionFilteringProvider`. It is designed to remove `Collection` or array elements for which a principal does not have access. It never thrown an `AccessDeniedException` - simply silently removes the offending elements. The provider is configured as follows:

    <bean id="afterAclCollectionRead" class="org.acegisecurity.afterinvocation.BasicAclEntryAfterInvocationCollectionFilteringProvider">
      <property name="aclManager"><ref local="aclManager"/></property>
      <property name="requirePermission">
        <list>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.ADMINISTRATION"/>
          <ref local="org.acegisecurity.acl.basic.SimpleAclEntry.READ"/>
        </list>
      </property>
    </bean>

As you can imagine, the returned `Object` must be a `Collection` or array for this provider to operate. It will remove any element if the `AclManager` indicates the `Authentication` does not hold one of the listed `requirePermission`s.

The Contacts sample application demonstrates these two `AfterInvocationProvider`s.

## 1.9. Run-As Authentication Replacement

### 1.9.1. Purpose

The `AbstractSecurityInterceptor` is able to temporarily replace the `Authentication` object in the `SecurityContext` and `SecurityContextHolder` during the `SecurityInterceptorCallback`. This only occurs if the original `Authentication` object was successfully processed by the `AuthenticationManager` and `AccessDecisionManager`. The `RunAsManager` will indicate the replacement `Authentication` object, if any, that should be used during the `SecurityInterceptorCallback`.

By temporarily replacing the `Authentication` object during a `SecurityInterceptorCallback`, the secured invocation will be able to call other objects which require different authentication and authorization credentials. It will also be able to perform any internal security checks for specific `GrantedAuthority` objects. Because Acegi Security provides a number of helper classes that automatically configure remoting protocols based on the contents of the `ContextHolder`, these run-as replacements are particularly useful when calling remote web services.

### 1.9.2. Usage

A `RunAsManager` interface is provided by the Acegi Security System for Spring:

    public Authentication buildRunAs(Authentication authentication, Object object, ConfigAttributeDefinition config);
    public boolean supports(ConfigAttribute attribute);
    public boolean supports(Class clazz);

The first method returns the `Authentication` object that should replace the existing `Authentication` object for the duration of the method invocation. If the method returns `null`, it indicates no replacement should be made. The second method is used by the `AbstractSecurityInterceptor` as part of its startup validation of configuration attributes. The `supports(Class)` method is called by a security interceptor implementation to ensure the configured `RunAsManager` supports the type of secure object that the security interceptor will present.

One concrete implementation of a `RunAsManager` is provided with the Acegi Security System for Spring. The `RunAsManagerImpl` class returns a replacement `RunAsUserToken` if any `ConfigAttribute` starts with `RUN_AS_`. If any such `ConfigAttribute` is found, the replacement `RunAsUserToken` will contain the same principal, credentials and granted authorities as the original `Authentication` object, along with a new `GrantedAuthorityImpl` for each `RUN_AS_` `ConfigAttribute`. Each new `GrantedAuthorityImpl` will be prefixed with `ROLE_`, followed by the `RUN_AS` `ConfigAttribute`. For example, a `RUN_AS_SERVER` will result in the replacement `RunAsUserToken` containing a `ROLE_RUN_AS_SERVER` granted authority.

The replacement `RunAsUserToken` is just like any other `Authentication` object. It needs to be authenticated by the `AuthenticationManager`, probably via delegation to a suitable `AuthenticationProvider`. The `RunAsImplAuthenticationProvider` performs such authentication. It simply accepts as valid any `RunAsUserToken` presented.

To ensure malicious code does not create a `RunAsUserToken` and present it for guaranteed acceptance by the `RunAsImplAuthenticationProvider`, the hash of a key is stored in all generated tokens. The `RunAsManagerImpl` and `RunAsImplAuthenticationProvider` is created in the bean context with the same key:

    <bean id="runAsManager" class="org.acegisecurity.runas.RunAsManagerImpl">
      <property name="key"><value>my_run_as_password</value></property>
    </bean>

    <bean id="runAsAuthenticationProvider" class="org.acegisecurity.runas.RunAsImplAuthenticationProvider">
      <property name="key"><value>my_run_as_password</value></property>
    </bean>

By using the same key, each `RunAsUserToken` can be validated it was created by an approved `RunAsManagerImpl`. The `RunAsUserToken` is immutable after creation for security reasons.

## 1.10. User Interfacing with the SecurityContextHolder

### 1.10.1. Purpose

Everything presented so far assumes one thing: the `SecurityContextHolder` is populated with a valid `SecurityContext`, which in turn contains a valid `Authentication` object. Developers are free to do this in whichever way they like, such as directly calling the relevant objects at runtime. However, several classes have been provided to make this process transparent in many situations. We call these classes "authentication mechanisms".

The `org.acegisecurity.ui` package provides what we call "authentication processing mechanisms". An authentication processing mechanism is solely concerned with received an authentication request from the principal, testing if it seems valid, and if so, placing the authentication request token onto the `SecurityContextHolder`. Of course, if the authentication request is invalid, the authentication processing mechanism is responsible for informing the principal in whatever way is appropriate to the protocol.

Recall the `HttpSessionContextIntegrationFilter` (discussed in the context section) is responsible for storing the `SecurityContextHolder` contents between invocations. This means no authentication processing mechanism need ever interact directly with `HttpSession`. Indeed `HttpSessionContextIntegrationFilter` has been designed to minimise the unnecessary creation of `HttpSession`s, as might occur when using Basic authentication for example.

There are several authentication processing mechanisms included with Acegi Security, which will be briefly discussed in this chapter. The most popular (and almost always recommended) approach is HTTP Form Authentication, which uses a login form to authenticate the user. Another approach (commonly use with web services) is HTTP Basic Authentication, which allows clients to use HTTP headers to present authentication information to the Acegi Security System for Spring. Alternatively, you can also use Yale Central Authentication Service (CAS) for enterprise-wide single sign on. The final (and generally unrecommended) approach is via Container Adapters, which allow supported web containers to perform the authentication themselves. HTTP Form Authentication and Basic Authentication is discussed below, whilst CAS and Container Adapters are discussed in separate sections of this document.

### 1.10.2. HTTP Form Authentication

HTTP Form Authentication involves using the `AuthenticationProcessingFilter` to process a login form. The login form simply contains `j_username` and `j_password` input fields, and posts to a URL that is monitored by the filter (by default `j_acegi_security_check`). The filter is defined in `web.xml` behind a `FilterToBeanProxy` as follows:

    <filter>
      <filter-name>Acegi Authentication Processing Filter</filter-name>
      <filter-class>org.acegisecurity.util.FilterToBeanProxy</filter-class>
      <init-param>
        <param-name>targetClass</param-name>
        <param-value>org.acegisecurity.ui.webapp.AuthenticationProcessingFilter</param-value>
      </init-param>
    </filter>

    <filter-mapping>
      <filter-name>Acegi Authentication Processing Filter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

For a discussion of `FilterToBeanProxy`, please refer to the Filters section. The application context will need to define the `AuthenticationProcessingFilter`:

    <bean id="authenticationProcessingFilter" class="org.acegisecurity.ui.webapp.AuthenticationProcessingFilter">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="authenticationFailureUrl"><value>/acegilogin.jsp?login_error=1</value></property>
      <property name="defaultTargetUrl"><value>/</value></property>
      <property name="filterProcessesUrl"><value>/j_acegi_security_check</value></property>
    </bean>

The configured `AuthenticationManager` processes each authentication request. If authentication fails, the browser will be redirected to the `authenticationFailureUrl`. The `AuthenticationException` will be placed into the `HttpSession` attribute indicated by `AbstractProcessingFilter.ACEGI_SECURITY_LAST_EXCEPTION_KEY`, enabling a reason to be provided to the user on the error page.

If authentication is successful, the resulting `Authentication` object will be placed into the `SecurityContextHolder`.

Once the `SecurityContextHolder` has been updated, the browser will need to be redirected to the target URL. The target URL is usually indicated by the `HttpSession` attribute specified by `AbstractProcessingFilter.ACEGI_SECURITY_TARGET_URL_KEY`. This attribute is automatically set by the `SecurityEnforcementFilter` when an `AuthenticationException` occurs, so that after login is completed the user can return to what they were trying to access. If for some reason the `HttpSession` does not indicate the target URL, the browser will be redirected to the `defaultTargetUrl` property.

Because this authentication approach is fully contained within a single web application, HTTP Form Authentication is recommended to be used instead of Container Adapters.

### 1.10.3. HTTP Basic Authentication

The Acegi Security System for Spring provides a `BasicProcessingFilter` which is capable of processing basic authentication credentials presented in HTTP headers. This can be used for authenticating calls made by Spring remoting protocols (such as Hessian and Burlap), as well as normal user agents (such as Internet Explorer and Navigator). The standard governing HTTP Basic Authentication is defined by RFC 1945, Section 11, and the `BasicProcessingFilter` conforms with this RFC. Basic Authentication is an attractive approach to authentication, because it is very widely deployed in user agents and implementation is extremely simple (it's just a Base64 encoding of the username:password, specified in a HTTP header).

To implement HTTP Basic Authentication, it is necessary to define `BasicProcessingFilter` in the fitler chain. The application context will need to define the `BasicProcessingFilter` and its required collaborator:

    <bean id="basicProcessingFilter" class="org.acegisecurity.ui.basicauth.BasicProcessingFilter">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="authenticationEntryPoint"><ref bean="authenticationEntryPoint"/></property>
    </bean>

    <bean id="authenticationEntryPoint" class="org.acegisecurity.ui.basicauth.BasicProcessingFilterEntryPoint">
      <property name="realmName"><value>Name Of Your Realm</value></property>
    </bean>

The configured `AuthenticationManager` processes each authentication request. If authentication fails, the configured `AuthenticationEntryPoint` will be used to retry the authentication process. Usually you will use the `BasicProcessingFilterEntryPoint`, which returns a 401 response with a suitable header to retry HTTP Basic authentication. If authentication is successful, the resulting `Authentication` object will be placed into the `SecurityContextHolder`.

If the authentication event was successful, or authentication was not attempted because the HTTP header did not contain a supported authentication request, the filter chain will continue as normal. The only time the filter chain will be interrupted is if authentication fails and the `AuthenticationEntryPoint` is called, as discussed in the previous paragraph.

### 1.10.4. HTTP Digest Authentication

The Acegi Security System for Spring provides a `DigestProcessingFilter` which is capable of processing digest authentication credentials presented in HTTP headers. Digest Authentication attempts to solve many of the weakenesses of Basic authentication, specifically by ensuring credentials are never sent in clear text across the wire. Many user agents support Digest Authentication, including FireFox and Internet Explorer. The standard governing HTTP Digest Authentication is defined by RFC 2617, which updates an earlier version of the Digest Authentication standard prescribed by RFC 2069. Most user agents implement RFC 2617. The Acegi Security `DigestProcessingFilter` is compatible with the "`auth`" quality of protection (`qop`) prescribed by RFC 2617, which also provides backward compatibility with RFC 2069. Digest Authentication is a highly attractive option if you need to use unencrypted HTTP (ie no TLS/HTTPS) and wish to maximise security of the authentication process. Indeed Digest Authentication is a mandatory requirement for the WebDAV protocol, as noted by RFC 2518 Section 17.1, so we should expect to see it increasingly deployed and replacing Basic Authentication.

Digest Authentication is definitely the most secure choice between Form Authentication, Basic Authentication and Digest Authentication, although extra security also means more complex user agent implementations. Central to Digest Authentication is a "nonce". This is a value the server generates. Acegi Security's nonce adopts the following format:

    base64(expirationTime + ":" + md5Hex(expirationTime + ":" + key))

    expirationTime:   The date and time when the nonce expires, expressed in milliseconds
    key:              A private key to prevent modification of the nonce token

The `DigestProcessingFilterEntryPoint` has a property specifying the `key` used for generating the nonce tokens, along with a `nonceValiditySeconds` property for determining the expiration time (default 300, which equals five minutes). Whilstever the nonce is valid, the digest is computed by concatenating various strings including the username, password, nonce, URI being requested, a client-generated nonce (merely a random value which the user agent generates each request), the realm name etc, then performing an MD5 hash. Both the server and user agent perform this digest computation, resulting in different hash codes if they disagree on an included value (eg password). In the Acegi Security implementation, if the server-generated nonce has merely expired (but the digest was otherwise valid), the `DigestProcessingFilterEntryPoint` will send a `"stale=true"` header. This tells the user agent there is no need to disturb the user (as the password and username etc is correct), but simply to try again using a new nonce.

An appropriate value for `DigestProcessingFilterEntryPoint`'s `nonceValiditySeconds` parameter will depend on your application. Extremely secure applications should note that an intercepted authentication header can be used to impersonate the principal until the `expirationTime` contained in the nonce is reached. This is the key principle when selecting an appropriate setting, but it would be unusual for immensly secure applications to not be running over TLS/HTTPS in the first instance.

Because of the more complex implementation of Digest Authentication, there are often user agent issues. For example, Internet Explorer fails to present an "`opaque`" token on subsequent requests in the same session. The Acegi Security filters therefore encapsulate all state information into the "`nonce`" token instead. In our testing, the Acegi Security implementation works reliably with FireFox and Internet Explorer, correctly handling nonce timeouts etc.

Now that we've reviewed the theory, let's see how to use it. To implement HTTP Digest Authentication, it is necessary to define `DigestProcessingFilter` in the fitler chain. The application context will need to define the `DigestProcessingFilter` and its required collaborators:

    <bean id="digestProcessingFilter" class="org.acegisecurity.ui.digestauth.DigestProcessingFilter">
      <property name="userDetailsService"><ref local="jdbcDaoImpl"/></property>
      <property name="authenticationEntryPoint"><ref local="digestProcessingFilterEntryPoint"/></property>
      <property name="userCache"><ref local="userCache"/></property>
    </bean>

    <bean id="digestProcessingFilterEntryPoint" class="org.acegisecurity.ui.digestauth.DigestProcessingFilterEntryPoint">
      <property name="realmName"><value>Contacts Realm via Digest Authentication</value></property>
      <property name="key"><value>acegi</value></property>
      <property name="nonceValiditySeconds"><value>10</value></property>
    </bean>

The configured `UserDetailsService` is needed because `DigestProcessingFilter` must have direct access to the clear text password of a user. Digest Authentication will NOT work if you are using encoded passwords in your DAO. The DAO collaborator, along with the `UserCache`, are typically shared directly with a `DaoAuthenticationProvider`. The `authenticationEntryPoint` property must be `DigestProcessingFilterEntryPoint`, so that `DigestProcessingFilter` can obtain the correct `realmName` and `key` for digest calculations.

Like `BasicAuthenticationFilter`, if authentication is successful an `Authentication` request token will be placed into the `SecurityContextHolder`. If the authentication event was successful, or authentication was not attempted because the HTTP header did not contain a Digest Authentication request, the filter chain will continue as normal. The only time the filter chain will be interrupted is if authentication fails and the `AuthenticationEntryPoint` is called, as discussed in the previous paragraph.

Digest Authentication's RFC offers a range of additional features to further increase security. For example, the nonce can be changed on every request. Despite this, the Acegi Security implementation was designed to minimise the complexity of the implementation (and the doubtless user agent incompatibilities that would emerge), and avoid needing to store server-side state. You are invited to review RFC 2617 if you wish to explore these features in more detail. As far as we are aware, the Acegi Security implementation does comply with the minimum standards of this RFC.

### 1.10.5. Anonymous Authentication

Particularly in the case of web request URI security, sometimes it is more convenient to assign configuration attributes against every possible secure object invocation. Put differently, sometimes it is nice to say `ROLE_SOMETHING` is required by default and only allow certain exceptions to this rule, such as for login, logout and home pages of an application. There are also other situations where anonymous authentication would be desired, such as when an auditing interceptor queries the `SecurityContextHolder` to identify which principal was responsible for a given operation. Such classes can be authored with more robustness if they know the `SecurityContextHolder` always contains an `Authentication` object, and never `null`.

Acegi Security provides three classes that together provide an anoymous authentication feature. `AnonymousAuthenticationToken` is an implementation of `Authentication`, and stores the `GrantedAuthority`[]s which apply to the anonymous principal. There is a corresponding `AnonymousAuthenticationProvider`, which is chained into the `ProviderManager` so that `AnonymousAuthenticationTokens` are accepted. Finally, there is an AnonymousProcessingFilter, which is chained after the normal authentication mechanisms and automatically add an `AnonymousAuthenticationToken` to the `SecurityContextHolder` if there is no existing `Authentication` held there. The definition of the filter and authentication provider appears as follows:

    <bean id="anonymousProcessingFilter" class="org.acegisecurity.providers.anonymous.AnonymousProcessingFilter">
      <property name="key"><value>foobar</value></property>
      <property name="userAttribute"><value>anonymousUser,ROLE_ANONYMOUS</value></property>
    </bean>

    <bean id="anonymousAuthenticationProvider" class="org.acegisecurity.providers.anonymous.AnonymousAuthenticationProvider">
      <property name="key"><value>foobar</value></property>
    </bean>

The `key` is shared between the filter and authentication provider, so that tokens created by the former are accepted by the latter. The `userAttribute` is expressed in the form of `usernameInTheAuthenticationToken,grantedAuthority[,grantedAuthority]`. This is the same syntax as used after the equals sign for `InMemoryDaoImpl`'s `userMap` property.

As explained earlier, the benefit of anonymous authentication is that all URI patterns can have security applied to them. For example:

    <bean id="filterInvocationInterceptor" class="org.acegisecurity.intercept.web.FilterSecurityInterceptor">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="accessDecisionManager"><ref local="httpRequestAccessDecisionManager"/></property>
      <property name="objectDefinitionSource">
        <value>
          CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
          PATTERN_TYPE_APACHE_ANT
          /index.jsp=ROLE_ANONYMOUS,ROLE_USER
          /hello.htm=ROLE_ANONYMOUS,ROLE_USER
          /logoff.jsp=ROLE_ANONYMOUS,ROLE_USER
          /acegilogin.jsp*=ROLE_ANONYMOUS,ROLE_USER
          /**=ROLE_USER
        </value>
      </property>
    </bean>

Rounding out the anonymous authentication discussion is the `AuthenticationTrustResolver` interface, with its corresponding `AuthenticationTrustResolverImpl` implementation. This interface provides an `isAnonymous(Authentication)` method, which allows interested classes to take into account this special type of authentication status. The `SecurityEnforcementFilter` uses this interface in processing `AccessDeniedException`s. If an `AccessDeniedException` is thrown, and the authentication is of an anonymous type, instead of throwing a 403 (forbidden) response, the filter will instead commence the `AuthenticationEntryPoint` so the principal can authenticate properly. This is a necessary distinction, otherwise principals would always be deemed "authenticated" and never be given an opportunity to login via form, basic, digest or some other normal authentication mechanism.

### 1.10.6. Remember-Me Authentication

Remember-me authentication refers to web sites being able to remember the identity of a principal between sessions. This is typically accomplished by sending a cookie to the browser, with the cookie being detected during future sessions and causing automated login to take place. Acegi Security provides the necessary hooks so that such operations can take place, along with providing a concrete implementation that uses hashing to preserve the security of cookie-based tokens.

Remember-me authentication is not used with digest or basic authentication, given they are often not used with `HttpSession`s. Remember-me is used with `AuthenticationProcessingFilter`, and is implemented via hooks in the `AbstractProcessingFilter` superclass. The hooks will invoke a concrete `RememberMeServices` at the appropriate times. The interface looks like this:

    public Authentication autoLogin(HttpServletRequest request, HttpServletResponse response);
    public void loginFail(HttpServletRequest request, HttpServletResponse response);
    public void loginSuccess(HttpServletRequest request, HttpServletResponse response, Authentication successfulAuthentication);

Please refer to JavaDocs for a fuller discussion on what the methods do, although note at this stage `AbstractProcessingFilter` only calls the `loginFail()` and `loginSuccess()` methods. The `autoLogin()` method is called by `RememberMeProcessingFilter` whenever the `SecurityContextHolder` does not contain an `Authentication`. This interface therefore provides the underlaying remember-me implementation with sufficient notification of authentication-related events, and delegates to the implementation whenever a candidate web request might contain a cookie and wish to be remembered.

This design allows any number of remember-me implementation strategies. In the interests of simplicity and avoiding the need for DAO implementations that specify write and create methods, Acegi Security's only concrete implementation, `TokenBasedRememberMeServices`, uses hashing to achieve a useful remember-me strategy. In essence a cookie is sent to the browser upon successful interactive authentication, with that cookie being composed as follows:

    base64(username + ":" + expirationTime + ":" + md5Hex(username + ":" + expirationTime + ":" password + ":" + key))

    username:         As identifiable to TokenBasedRememberMeServices.getUserDetailsService()
    password:         That matches the relevant UserDetails retrieved from TokenBasedRememberMeServices.getUserDetailsService()
    expirationTime:   The date and time when the remember-me token expires, expressed in milliseconds
    key:              A private key to prevent modification of the remember-me token

As such the remember-me token is valid only for the period specified, and provided that the username, password and key does not change. Notably, this has a potential security issue issue in that a captured remember-me token will be usable from any user agent until such time as the token expires. This is the same issue as with digest authentication. If a principal is aware a token has been captured, they can easily change their password and immediately invalidate all remember-me tokens on issue. However, if more significant security is needed a rolling token approach should be used (this would require a database) or remember-me services should simply not be used.

`TokenBasedRememberMeServices` generates a `RememberMeAuthenticationToken`, which is processed by `RememberMeAuthenticationProvider`. A `key` is shared between this authentication provider and the `TokenBasedRememberMeServices`. In addition, `TokenBasedRememberMeServices` requires A UserDetailsService from which it can retrieve the username and password for signature comparison purposes, and generate the `RememberMeAuthenticationToken` to contain the correct `GrantedAuthority`[]s. Some sort of logout command should be provided by the application (typically via a JSP) that invalidates the cookie upon user request. See the Contacts Sample application's `logout.jsp` for an example.

The beans required in an application context to enable remember-me services are as follows:

    <bean id="rememberMeProcessingFilter" class="org.acegisecurity.ui.rememberme.RememberMeProcessingFilter">
      <property name="rememberMeServices"><ref local="rememberMeServices"/></property>
    </bean>

    <bean id="rememberMeServices" class="org.acegisecurity.ui.rememberme.TokenBasedRememberMeServices">
      <property name="userDetailsService"><ref local="jdbcDaoImpl"/></property>
      <property name="key"><value>springRocks</value></property>
    </bean>

    <bean id="rememberMeAuthenticationProvider" class="org.acegisecurity.providers.rememberme.RememberMeAuthenticationProvider">
      <property name="key"><value>springRocks</value></property>
    </bean>

Don't forget to add your `RememberMeServices` implementation to your `AuthenticationProcessingFilter.setRememberMeServices()` property, include the `RememberMeAuthenticationProvider` in your `AuthenticationManager.setProviders()` list, and add a call to `RememberMeProcessingFilter` into your `FilterChainProxy` (typically immediately after your `AuthenticationProcessingFilter`).

### 1.10.7. Well-Known Locations

Prior to release 0.8.0, Acegi Security referred to "well-known locations" in discussions about storing the `Authentication`. This approach did not explicitly separate the function of `HttpSession` storage of `SecurityContextHolder` contents from the processing of authentication requests received through various protocols. In addition, the previous approach did not facilitate storage of non-`Authentication` objects between requests, which was limiting usefulness of the `SecurityContextHolder` system to member of the community. For these reasons, the notion of well-known locations was abandoned, the `HttpSessionContextIntegrationFilter` was established, and the purpose of authentication processing mechanisms was explicitly defined and limited to interaction with the `SecurityContextHolder` only. There is no need to refer to well-known locations any more and we hope this clearer separation of responsibilities enhances understanding of the design.

## 1.11. Container Adapters

### 1.11.1. Overview

Very early versions of the Acegi Security System for Spring exclusively used Container Adapters for interfacing authentication with end users. Whilst this worked well, it required considerable time to support multiple container versions and the configuration itself was relatively time-consuming for developers. For this reason the HTTP Form Authentication and HTTP Basic Authentication approaches were developed, and are today recommended for almost all applications.

Container Adapters enable the Acegi Security System for Spring to integrate directly with the containers used to host end user applications. This integration means that applications can continue to leverage the authentication and authorization capabilities built into containers (such as `isUserInRole()` and form-based or basic authentication), whilst benefiting from the enhanced security interception capabilities provided by the Acegi Security System for Spring (it should be noted that Acegi Security also offers `ContextHolderAwareRequestWrapper` to deliver `isUserInRole()` and similar Servlet Specification compatibility methods).

The integration between a container and the Acegi Security System for Spring is achieved through an adapter. The adapter provides a container-compatible user authentication provider, and needs to return a container-compatible user object.

The adapter is instantiated by the container and is defined in a container-specific configuration file. The adapter then loads a Spring application context which defines the normal authentication manager settings, such as the authentication providers that can be used to authenticate the request. The application context is usually named `acegisecurity.xml` and is placed in a container-specific location.

The Acegi Security System for Spring currently supports Jetty, Catalina (Tomcat), JBoss and Resin. Additional container adapters can easily be written.

### 1.11.2. Adapter Authentication Provider

As is always the case, the container adapter generated `Authentication` object still needs to be authenticated by an `AuthenticationManager` when requested to do so by the `AbstractSecurityInterceptor`. The `AuthenticationManager` needs to be certain the adapter-provided `Authentication` object is valid and was actually authenticated by a trusted adapter.

Adapters create `Authentication` objects which are immutable and implement the `AuthByAdapter` interface. These objects store the hash of a key that is defined by the adapter. This allows the `Authentication` object to be validated by the `AuthByAdapterProvider`. This authentication provider is defined as follows:

    <bean id="authByAdapterProvider" class="org.acegisecurity.adapters.AuthByAdapterProvider">
      <property name="key"><value>my_password</value></property>
    </bean>

The key must match the key that is defined in the container-specific configuration file that starts the adapter. The `AuthByAdapterProvider` automatically accepts as valid any `AuthByAdapter` implementation that returns the expected hash of the key.

To reiterate, this means the adapter will perform the initial authentication using providers such as `DaoAuthenticationProvider`, returning an `AuthByAdapter` instance that contains a hash code of the key. Later, when an application calls a security interceptor managed resource, the `AuthByAdapter` instance in the `SecurityContext` in the `SecurityContextHolder` will be tested by the application's `AuthByAdapterProvider`. There is no requirement for additional authentication providers such as `DaoAuthenticationProvider` within the application-specific application context, as the only type of `Authentication` instance that will be presented by the application is from the container adapter.

Classloader issues are frequent with containers and the use of container adapters illustrates this further. Each container requires a very specific configuration. The installation instructions are provided below. Once installed, please take the time to try the sample application to ensure your container adapter is properly configured.

When using container adapters with the `DaoAuthenticationProvider`, ensure you set its `forcePrincipalAsString` property to `true`.

### 1.11.3. Catalina (Tomcat) Installation

The following was tested with Jakarta Tomcat 4.1.30 and 5.0.19.

`$CATALINA_HOME` refers to the root of your Catalina (Tomcat) installation.

Edit your `$CATALINA_HOME/conf/server.xml` file so the `<Engine>` section contains only one active `<Realm>` entry. An example realm entry:

          <Realm className="org.acegisecurity.adapters.catalina.CatalinaAcegiUserRealm"
                 appContextLocation="conf/acegisecurity.xml"
                 key="my_password" />

Be sure to remove any other `<Realm>` entry from your `<Engine>` section.

Copy `acegisecurity.xml` into `$CATALINA_HOME/conf`.

Copy `acegi-security-catalina-XX.jar` into `$CATALINA_HOME/server/lib`.

Copy the following files into `$CATALINA_HOME/common/lib`:

- `aopalliance.jar`

- `spring.jar`

- `commons-codec.jar`

- `burlap.jar`

- `hessian.jar`

None of the above JAR files (or `acegi-security-XX.jar`) should be in your application's `WEB-INF/lib`. The realm name indicated in your `web.xml` does not matter with Catalina.

We have received reports of problems using this Container Adapter with Mac OS X. A work-around is to use a script such as follows:

    #!/bin/sh
    export CATALINA_HOME="/Library/Tomcat"
    export JAVA_HOME="/Library/Java/Home"
    cd /
    $CATALINA_HOME/bin/startup.sh

### 1.11.4. Jetty Installation

The following was tested with Jetty 4.2.18.

`$JETTY_HOME` refers to the root of your Jetty installation.

Edit your `$JETTY_HOME/etc/jetty.xml` file so the `<Configure class>` section has a new addRealm call:

      <Call name="addRealm">
        <Arg>
          <New class="org.acegisecurity.adapters.jetty.JettyAcegiUserRealm">
            <Arg>Spring Powered Realm</Arg>
            <Arg>my_password</Arg>
            <Arg>etc/acegisecurity.xml</Arg>
          </New>
        </Arg>
      </Call>

Copy `acegisecurity.xml` into `$JETTY_HOME/etc`.

Copy the following files into `$JETTY_HOME/ext`:

- `aopalliance.jar`

- `commons-logging.jar`

- `spring.jar`

- `acegi-security-jetty-XX.jar`

- `commons-codec.jar`

- `burlap.jar`

- `hessian.jar`

None of the above JAR files (or `acegi-security-XX.jar`) should be in your application's `WEB-INF/lib`. The realm name indicated in your `web.xml` does matter with Jetty. The `web.xml` must express the same `<realm-name>` as your `jetty.xml` (in the example above, "Spring Powered Realm").

### 1.11.5. JBoss Installation

The following was tested with JBoss 3.2.6.

`$JBOSS_HOME` refers to the root of your JBoss installation.

There are two different ways of making spring context available to the Jboss integration classes.

The first approach is by editing your `$JBOSS_HOME/server/your_config/conf/login-config.xml` file so that it contains a new entry under the `<Policy>` section:

        <application-policy name = "SpringPoweredRealm">
           <authentication>
              <login-module code = "org.acegisecurity.adapters.jboss.JbossSpringLoginModule"
                flag = "required">
                <module-option name = "appContextLocation">acegisecurity.xml</module-option>
                <module-option name = "key">my_password</module-option>
             </login-module>
           </authentication>
        </application-policy>

Copy `acegisecurity.xml` into `$JBOSS_HOME/server/your_config/conf`.

In this configuration `acegisecurity.xml` contains the spring context definition including all the authentication manager beans. You have to bear in mind though, that `SecurityContext` is created and destroyed on each login request, so the login operation might become costly. Alternatively, the second approach is to use Spring singleton capabilities through `org.springframework.beans.factory.access.SingletonBeanFactoryLocator`. The required configuration for this approach is:

        <application-policy name = "SpringPoweredRealm">
           <authentication>
              <login-module code = "org.acegisecurity.adapters.jboss.JbossSpringLoginModule"
                flag = "required">
                <module-option name = "singletonId">springRealm</module-option>
                <module-option name = "key">my_password</module-option>
                <module-option name = "authenticationManager">authenticationManager</module-option>
             </login-module>
           </authentication>
        </application-policy>

In the above code fragment, `authenticationManager` is a helper property that defines the expected name of the `AuthenticationManager` in case you have several defined in the IoC container. The `singletonId` property references a bean defined in a `beanRefFactory.xml` file. This file needs to be available from anywhere on the JBoss classpath, including `$JBOSS_HOME/server/your_config/conf`. The `beanRefFactory.xml` contains the following declaration:

    <beans>
      <bean id="springRealm" singleton="true" lazy-init="true" class="org.springframework.context.support.ClassPathXmlApplicationContext">
        <constructor-arg>
          <list>
            <value>acegisecurity.xml</value>
          </list>
        </constructor-arg>
      </bean>
    </beans>

Finally, irrespective of the configuration approach you need to copy the following files into `$JBOSS_HOME/server/your_config/lib`:

- `aopalliance.jar`

- `spring.jar`

- `acegi-security-jboss-XX.jar`

- `commons-codec.jar`

- `burlap.jar`

- `hessian.jar`

None of the above JAR files (or `acegi-security-XX.jar`) should be in your application's `WEB-INF/lib`. The realm name indicated in your `web.xml` does not matter with JBoss. However, your web application's `WEB-INF/jboss-web.xml` must express the same `<security-domain>` as your `login-config.xml`. For example, to match the above example, your `jboss-web.xml` would look like this:

    <jboss-web>
      <security-domain>java:/jaas/SpringPoweredRealm</security-domain>
    </jboss-web>

### 1.11.6. Resin Installation

The following was tested with Resin 3.0.6.

`$RESIN_HOME` refers to the root of your Resin installation.

Resin provides several ways to support the container adapter. In the instructions below we have elected to maximise consistency with other container adapter configurations. This will allow Resin users to simply deploy the sample application and confirm correct configuration. Developers comfortable with Resin are naturally able to use its capabilities to package the JARs with the web application itself, and/or support single sign-on.

Copy the following files into `$RESIN_HOME/lib`:

- `aopalliance.jar`

- `commons-logging.jar`

- `spring.jar`

- `acegi-security-resin-XX.jar`

- `commons-codec.jar`

- `burlap.jar`

- `hessian.jar`

Unlike the container-wide `acegisecurity.xml` files used by other container adapters, each Resin web application will contain its own `WEB-INF/resin-acegisecurity.xml` file. Each web application will also contain a `resin-web.xml` file which Resin uses to start the container adapter:

    <web-app>
      <authenticator>
        <type>org.acegisecurity.adapters.resin.ResinAcegiAuthenticator</type>
        <init>
          <app-context-location>WEB-INF/resin-acegisecurity.xml</app-context-location>
          <key>my_password</key>
        </init>
      </authenticator>
    </web-app>

With the basic configuration provided above, none of the JAR files listed (or `acegi-security-XX.jar`) should be in your application's `WEB-INF/lib`. The realm name indicated in your `web.xml` does not matter with Resin, as the relevant authentication class is indicated by the `<authenticator>` setting.

## 1.12. Yale Central Authentication Service (CAS) Single Sign On

### 1.12.1. Overview

Yale University produces an enterprise-wide single sign on system known as CAS. Unlike other initiatives, Yale's Central Authentication Service is open source, widely used, simple to understand, platform independent, and supports proxy capabilities. The Acegi Security System for Spring fully supports CAS, and provides an easy migration path from single-application deployments of Acegi Security through to multiple-application deployments secured by an enterprise-wide CAS server.

You can learn more about CAS at `http://www.yale.edu/tp/auth/`. You will need to visit this URL to download the CAS Server files. Whilst the Acegi Security System for Spring includes two CAS libraries in the "-with-dependencies" ZIP file, you will still need the CAS Java Server Pages and `web.xml` to customise and deploy your CAS server.

### 1.12.2. How CAS Works

Whilst the CAS web site above contains two documents that detail the architecture of CAS, we present the general overview again here within the context of the Acegi Security System for Spring. The following refers to CAS 2.0, being the version of CAS that Acegi Security System for Spring supports.

Somewhere in your enterprise you will need to setup a CAS server. The CAS server is simply a standard WAR file, so there isn't anything difficult about setting up your server. Inside the WAR file you will customise the login and other single sign on pages displayed to users. You will also need to specify in the web.xml a `PasswordHandler`. The `PasswordHandler` has a simple method that returns a boolean as to whether a given username and password is valid. Your `PasswordHandler` implementation will need to link into some type of backend authentication repository, such as an LDAP server or database.

If you are already running an existing CAS server instance, you will have already established a `PasswordHandler`. If you do not already have a `PasswordHandler`, you might prefer to use the Acegi Security System for Spring `CasPasswordHandler` class. This class delegates through to the standard Acegi Security `AuthenticationManager`, enabling you to use a security configuration you might already have in place. You do not need to use the `CasPasswordHandler` class on your CAS server if you do not wish. The Acegi Security System for Spring will function as a CAS client successfully irrespective of the `PasswordHandler` you've chosen for your CAS server.

Apart from the CAS server itself, the other key player is of course the secure web applications deployed throughout your enterprise. These web applications are known as "services". There are two types of services: standard services and proxy services. A proxy service is able to request resources from other services on behalf of the user. This will be explained more fully later.

Services can be developed in a large variety of languages, due to CAS 2.0's very light XML-based protocol. The Yale CAS home page contains a clients archive which demonstrates CAS clients in Java, Active Server Pages, Perl, Python and others. Naturally, Java support is very strong given the CAS server is written in Java. You do not need to use any of CAS' client classes in applications secured by the Acegi Security System for Spring. This is handled transparently for you.

The basic interaction between a web browser, CAS server and an Acegi Security for System Spring secured service is as follows:

1. The web user is browsing the service's public pages. CAS or Acegi Security is not involved.

2. The user eventually requests a page that is either secure or one of the beans it uses is secure. Acegi Security's `SecurityEnforcementFilter` will detect the `AuthenticationException`.

3. Because the user's `Authentication` object (or lack thereof) caused an `AuthenticationException`, the `SecurityEnforcementFilter` will call the configured `AuthenticationEntryPoint`. If using CAS, this will be the `CasProcessingFilterEntryPoint` class.

4. The `CasProcessingFilterEntry` point will redirect the user's browser to the CAS server. It will also indicate a `service` parameter, which is the callback URL for the Acegi Security service. For example, the URL to which the browser is redirected might be `https://my.company.com/cas/login?service=https%3A%2F%2Fserver3.company.com%2Fwebapp%2Fj_acegi_cas_security_check`.

5. After the user's browser redirects to CAS, they will be prompted for their username and password. If the user presents a session cookie which indicates they've previously logged on, they will not be prompted to login again (there is an exception to this procedure, which we'll cover later). CAS will use the `PasswordHandler` discussed above to decide whether the username and password is valid.

6. Upon successful login, CAS will redirect the user's browser back to the original service. It will also include a `ticket` parameter, which is an opaque string representing the "service ticket". Continuing our earlier example, the URL the browser is redirected to might be `https://server3.company.com/webapp/j_acegi_cas_security_check?ticket=ST-0-ER94xMJmn6pha35CQRoZ`.

7. Back in the service web application, the `CasProcessingFilter` is always listening for requests to `/j_acegi_cas_security_check` (this is configurable, but we'll use the defaults in this introduction). The processing filter will construct a `UsernamePasswordAuthenticationToken` representing the service ticket. The principal will be equal to `CasProcessingFilter.CAS_STATEFUL_IDENTIFIER`, whilst the credentials will be the service ticket opaque value. This authentication request will then be handed to the configured `AuthenticationManager`.

8. The `AuthenticationManager` implementation will be the `ProviderManager`, which is in turn configured with the `CasAuthenticationProvider`. The `CasAuthenticationProvider` only responds to `UsernamePasswordAuthenticationToken`s containing the CAS-specific principal (such as `CasProcessingFilter.CAS_STATEFUL_IDENTIFIER`) and `CasAuthenticationToken`s (discussed later).

9. `CasAuthenticationProvider` will validate the service ticket using a `TicketValidator` implementation. Acegi Security includes one implementation, the `CasProxyTicketValidator`. This implementation a ticket validation class included in the CAS client library. The `CasProxyTicketValidator` makes a HTTPS request to the CAS server in order to validate the service ticket. The `CasProxyTicketValidator` may also include a proxy callback URL, which is included in this example: `https://my.company.com/cas/proxyValidate?service=https%3A%2F%2Fserver3.company.com%2Fwebapp%2Fj_acegi_cas_security_check&ticket=ST-0-ER94xMJmn6pha35CQRoZ&pgtUrl=https://server3.company.com/webapp/casProxy/receptor`.

10. Back on the CAS server, the proxy validation request will be received. If the presented service ticket matches the service URL the ticket was issued to, CAS will provide an affirmative response in XML indicating the username. If any proxy was involved in the authentication (discussed below), the list of proxies is also included in the XML response.

11. [OPTIONAL] If the request to the CAS validation service included the proxy callback URL (in the `pgtUrl` parameter), CAS will include a `pgtIou` string in the XML response. This `pgtIou` represents a proxy-granting ticket IOU. The CAS server will then create its own HTTPS connection back to the `pgtUrl`. This is to mutually authenticate the CAS server and the claimed service URL. The HTTPS connection will be used to send a proxy granting ticket to the original web application. For example, `https://server3.company.com/webapp/casProxy/receptor?pgtIou=PGTIOU-0-R0zlgrl4pdAQwBvJWO3vnNpevwqStbSGcq3vKB2SqSFFRnjPHt&pgtId=PGT-1-si9YkkHLrtACBo64rmsi3v2nf7cpCResXg5MpESZFArbaZiOKH`. We suggest you use CAS' `ProxyTicketReceptor` servlet to receive these proxy-granting tickets, if they are required.

12. The `CasProxyTicketValidator` will parse the XML received from the CAS server. It will return to the `CasAuthenticationProvider` a `TicketResponse`, which includes the username (mandatory), proxy list (if any were involved), and proxy-granting ticket IOU (if the proxy callback was requested).

13. Next `CasAuthenticationProvider` will call a configured `CasProxyDecider`. The `CasProxyDecider` indicates whether the proxy list in the `TicketResponse` is acceptable to the service. Several implementations are provided with the Acegi Security System: `RejectProxyTickets`, `AcceptAnyCasProxy` and `NamedCasProxyDecider`. These names are largely self-explanatory, except `NamedCasProxyDecider` which allows a `List` of trusted proxies to be provided.

14. `CasAuthenticationProvider` will next request a `CasAuthoritiesPopulator` to advise the `GrantedAuthority` objects that apply to the user contained in the `TicketResponse`. Acegi Security includes a `DaoCasAuthoritiesPopulator` which simply uses the `UserDetailsService` infrastructure to find the `UserDetails` and their associated `GrantedAuthority`s. Note that the password and enabled/disabled status of `UserDetails` returned by the `UserDetailsService` are ignored, as the CAS server is responsible for authentication decisions. `DaoCasAuthoritiesPopulator` is only concerned with retrieving the `GrantedAuthority`s.

15. If there were no problems, `CasAuthenticationProvider` constructs a `CasAuthenticationToken` including the details contained in the `TicketResponse` and the `GrantedAuthority`s. The `CasAuthenticationToken` contains the hash of a key, so that the `CasAuthenticationProvider` knows it created it.

16. Control then returns to `CasProcessingFilter`, which places the created `CasAuthenticationToken` into the `HttpSession` attribute named `HttpSessionIntegrationFilter.ACEGI_SECURITY_AUTHENTICATION_KEY`.

17. The user's browser is redirected to the original page that caused the `AuthenticationException`.

18. As the `Authentication` object is now in the well-known location, it is handled like any other authentication approach. Usually the `HttpSessionIntegrationFilter` will be used to associate the `Authentication` object with the `SecurityContextHolder` for the duration of each request.

It's good that you're still here! It might sound involved, but you can relax as the Acegi Security System for Spring classes hide much of the complexity. Let's now look at how this is configured.

### 1.12.3. CAS Server Installation (Optional)

As mentioned above, the Acegi Security System for Spring includes a `PasswordHandler` that bridges your existing `AuthenticationManager` into CAS. You do not need to use this `PasswordHandler` to use Acegi Security on the client side (any CAS `PasswordHandler` will do).

To install, you will need to download and extract the CAS server archive. We used version 2.0.12. There will be a `/web` directory in the root of the deployment. Copy an `applicationContext.xml` containing your `AuthenticationManager` as well as the `CasPasswordHandler` into the `/web/WEB-INF` directory. A sample `applicationContext.xml` is included below:

    <bean id="inMemoryDaoImpl" class="org.acegisecurity.userdetails.memory.InMemoryDaoImpl">
      <property name="userMap">
        <value>
          marissa=koala,ROLES_IGNORED_BY_CAS
          dianne=emu,ROLES_IGNORED_BY_CAS
          scott=wombat,ROLES_IGNORED_BY_CAS
          peter=opal,disabled,ROLES_IGNORED_BY_CAS
        </value>
      </property>
    </bean>

    <bean id="daoAuthenticationProvider" class="org.acegisecurity.providers.dao.DaoAuthenticationProvider">
      <property name="userDetailsService"><ref bean="inMemoryDaoImpl"/></property>
    </bean>

    <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
      <property name="providers">
        <list>
          <ref bean="daoAuthenticationProvider"/>
        </list>
      </property>
    </bean>

    <bean id="casPasswordHandler" class="org.acegisecurity.adapters.cas.CasPasswordHandler">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
    </bean>

Note the granted authorities are ignored by CAS because it has no way of communicating the granted authorities to calling applications. CAS is only concerned with username and passwords (and the enabled/disabled status).

Next you will need to edit the existing `/web/WEB-INF/web.xml` file. Add (or edit in the case of the `authHandler` property) the following lines:

    <context-param>
      <param-name>edu.yale.its.tp.cas.authHandler</param-name>
      <param-value>org.acegisecurity.adapters.cas.CasPasswordHandlerProxy</param-value>
    </context-param>

    <context-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/applicationContext.xml</param-value>
    </context-param>

    <listener>
      <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

Copy the `spring.jar` and `acegi-security.jar` files into `/web/WEB-INF/lib`. Now use the `ant dist` task in the `build.xml` in the root of the directory structure. This will create `/lib/cas.war`, which is ready for deployment to your servlet container.

Note CAS heavily relies on HTTPS. You can't even test the system without a HTTPS certificate. Whilst you should refer to your web container's documentation on setting up HTTPS, if you need some additional help or a test certificate you might like to check the `samples/contacts/etc/ssl` directory.

### 1.12.4. CAS Acegi Security System Client Installation

The web application side of CAS is made easy due to the Acegi Security System for Spring. It is assumed you already know the basics of using the Acegi Security System for Spring, so these are not covered again below. Only the CAS-specific beans are mentioned.

You will need to add a `ServiceProperties` bean to your application context. This represents your service:

    <bean id="serviceProperties" class="org.acegisecurity.ui.cas.ServiceProperties">
      <property name="service"><value>https://localhost:8443/contacts-cas/j_acegi_cas_security_check</value></property>
      <property name="sendRenew"><value>false</value></property>
    </bean>

The `service` must equal a URL that will be monitored by the `CasProcessingFilter`. The `sendRenew` defaults to false, but should be set to true if your application is particularly sensitive. What this parameter does is tell the CAS login service that a single sign on login is unacceptable. Instead, the user will need to re-enter their username and password in order to gain access to the service.

The following beans should be configured to commence the CAS authentication process:

    <bean id="casProcessingFilter" class="org.acegisecurity.ui.cas.CasProcessingFilter">
      <property name="authenticationManager"><ref bean="authenticationManager"/></property>
      <property name="authenticationFailureUrl"><value>/casfailed.jsp</value></property>
      <property name="defaultTargetUrl"><value>/</value></property>
      <property name="filterProcessesUrl"><value>/j_acegi_cas_security_check</value></property>
    </bean>

    <bean id="securityEnforcementFilter" class="org.acegisecurity.intercept.web.SecurityEnforcementFilter">
      <property name="filterSecurityInterceptor"><ref bean="filterInvocationInterceptor"/></property>
      <property name="authenticationEntryPoint"><ref bean="casProcessingFilterEntryPoint"/></property>
    </bean>

    <bean id="casProcessingFilterEntryPoint" class="org.acegisecurity.ui.cas.CasProcessingFilterEntryPoint">
      <property name="loginUrl"><value>https://localhost:8443/cas/login</value></property>
      <property name="serviceProperties"><ref bean="serviceProperties"/></property>
    </bean>

You will also need to add the `CasProcessingFilter` to web.xml:

    <filter>
      <filter-name>Acegi CAS Processing Filter</filter-name>
      <filter-class>org.acegisecurity.util.FilterToBeanProxy</filter-class>
      <init-param>
        <param-name>targetClass</param-name>
        <param-value>org.acegisecurity.ui.cas.CasProcessingFilter</param-value>
      </init-param>
    </filter>

    <filter-mapping>
      <filter-name>Acegi CAS Processing Filter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

The `CasProcessingFilter` has very similar properties to the `AuthenticationProcessingFilter` (used for form-based logins). Each property is self-explanatory.

For CAS to operate, the `SecurityEnforcementFilter` must have its `authenticationEntryPoint` property set to the `CasProcessingFilterEntryPoint` bean.

The `CasProcessingFilterEntryPoint` must refer to the `ServiceProperties` bean (discussed above), which provides the URL to the enterprise's CAS login server. This is where the user's browser will be redirected.

Next you need to add an `AuthenticationManager` that uses `CasAuthenticationProvider` and its collaborators:

    <bean id="authenticationManager" class="org.acegisecurity.providers.ProviderManager">
      <property name="providers">
        <list>
          <ref bean="casAuthenticationProvider"/>
        </list>
      </property>
    </bean>

    <bean id="casAuthenticationProvider" class="org.acegisecurity.providers.cas.CasAuthenticationProvider">
      <property name="casAuthoritiesPopulator"><ref bean="casAuthoritiesPopulator"/></property>
      <property name="casProxyDecider"><ref bean="casProxyDecider"/></property>
      <property name="ticketValidator"><ref bean="casProxyTicketValidator"/></property>
      <property name="statelessTicketCache"><ref bean="statelessTicketCache"/></property>
      <property name="key"><value>my_password_for_this_auth_provider_only</value></property>
    </bean>

    <bean id="casProxyTicketValidator" class="org.acegisecurity.providers.cas.ticketvalidator.CasProxyTicketValidator">
      <property name="casValidate"><value>https://localhost:8443/cas/proxyValidate</value></property>
      <property name="proxyCallbackUrl"><value>https://localhost:8443/contacts-cas/casProxy/receptor</value></property>
      <property name="serviceProperties"><ref bean="serviceProperties"/></property>
      <!-- <property name="trustStore"><value>/some/path/to/your/lib/security/cacerts</value></property> -->
    </bean>

    <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean">
      <property name="configLocation">
        <value>classpath:/ehcache-failsafe.xml</value>
      </property>
    </bean>

    <bean id="ticketCacheBackend" class="org.springframework.cache.ehcache.EhCacheFactoryBean">
      <property name="cacheManager">
        <ref local="cacheManager"/>
      </property>
      <property name="cacheName">
        <value>ticketCache</value>
      </property>
    </bean>

    <bean id="statelessTicketCache" class="org.acegisecurity.providers.cas.cache.EhCacheBasedTicketCache">
      <property name="cache"><ref local="ticketCacheBackend"/></property>
    </bean>

    <bean id="casAuthoritiesPopulator" class="org.acegisecurity.providers.cas.populator.DaoCasAuthoritiesPopulator">
      <property name="userDetailsService"><ref bean="inMemoryDaoImpl"/></property>
    </bean>

    <bean id="casProxyDecider" class="org.acegisecurity.providers.cas.proxy.RejectProxyTickets"/>

The beans are all reasonable self-explanatory if you refer back to the "How CAS Works" section. Careful readers might notice one surprise: the `statelessTicketCache` property of the `CasAuthenticationProvider`. This is discussed in detail in the "Advanced CAS Usage" section.

Note the `CasProxyTicketValidator` has a remarked out `trustStore` property. This property might be helpful if you experience HTTPS certificate issues. Also note the `proxyCallbackUrl` is set so the service can receive a proxy-granting ticket. As mentioned above, this is optional and unnecessary if you do not require proxy-granting tickets. If you do use this feature, you will need to configure a suitable servlet to receive the proxy-granting tickets. We suggest you use CAS' `ProxyTicketReceptor` by adding the following to your web application's `web.xml`:

    <servlet>
      <servlet-name>casproxy</servlet-name>
      <servlet-class>edu.yale.its.tp.cas.proxy.ProxyTicketReceptor</servlet-class>
    </servlet>

    <servlet-mapping>
      <servlet-name>casproxy</servlet-name>
      <url-pattern>/casProxy/*</url-pattern>
    </servlet-mapping>

This completes the configuration of CAS. If you haven't made any mistakes, your web application should happily work within the framework of CAS single sign on. No other parts of the Acegi Security System for Spring need to be concerned about the fact CAS handled authentication.

There is also a `contacts-cas.war` file in the sample applications directory. This sample application uses the above settings and can be deployed to see CAS in operation.

### 1.12.5. Advanced CAS Usage

The `CasAuthenticationProvider` distinguishes between stateful and stateless clients. A stateful client is considered any that originates via the `CasProcessingFilter`. A stateless client is any that presents an authentication request via the `UsernamePasswordAuthenticationToken` with a principal equal to `CasProcessingFilter.CAS_STATELESS_IDENTIFIER`.

Stateless clients are likely to be via remoting protocols such as Hessian and Burlap. The `BasicProcessingFilter` is still used in this case, but the remoting protocol client is expected to present a username equal to the static string above, and a password equal to a CAS service ticket. Clients should acquire a CAS service ticket directly from the CAS server.

Because remoting protocols have no way of presenting themselves within the context of a `HttpSession`, it isn't possible to rely on the `HttpSession`'s `HttpSessionIntegrationFilter.ACEGI_SECURITY_AUTHENTICATION_KEY` attribute to locate the `CasAuthenticationToken`. Furthermore, because the CAS server invalidates a service ticket after it has been validated by the `TicketValidator`, presenting the same service ticket on subsequent requests will not work. It is similarly very difficult to obtain a proxy-granting ticket for a remoting protocol client, as they are often deployed on client machines which rarely have HTTPS URLs that would be accessible to the CAS server.

One obvious option is to not use CAS at all for remoting protocol clients. However, this would eliminate many of the desirable features of CAS.

As a middle-ground, the `CasAuthenticationProvider` uses a `StatelessTicketCache`. This is used solely for requests with a principal equal to `CasProcessingFilter.CAS_STATELESS_IDENTIFIER`. What happens is the `CasAuthenticationProvider` will store the resulting `CasAuthenticationToken` in the `StatelessTicketCache`, keyed on the service ticket. Accordingly, remoting protocol clients can present the same service ticket and the `CasAuthenticationProvider` will not need to contact the CAS server for validation (aside from the first request).

The other aspect of advanced CAS usage involves creating proxy tickets from the proxy-granting ticket. As indicated above, we recommend you use CAS' `ProxyTicketReceptor` to receive these tickets. The `ProxyTicketReceptor` provides a static method that enables you to obtain a proxy ticket by presenting the proxy-granting IOU ticket. You can obtain the proxy-granting IOU ticket by calling `CasAuthenticationToken.getProxyGrantingTicketIou()`.

It is hoped you find CAS integration easy and useful with the Acegi Security System for Spring classes. Welcome to enterprise-wide single sign on!

## 1.13. X509 Authentication

### 1.13.1. Overview

The most common use of X509 certificate authentication is in verifying the identity of a server when using SSL, most commonly when using HTTPS from a browser. The browser will automatically check that the certificate presented by a server has been issued (ie digitally signed) by one of a list of trusted certificate authorities which it maintains.

You can also use SSL with “mutual authentication”; the server will then request a valid certificate from the client as part of the SSL handshake. The server will authenticate the client by checking that it's certificate is signed by an acceptable authority. If a valid certificate has been provided, it can be obtained through the servlet API in an application. The Acegi Security X509 module extracts the certificate using a filter and passes it to the configured X509 authentication provider to allow any additional application-specific checks to be applied. It also maps the certificate to an application user and loads that user's set of granted authorities for use with the standard Acegi Security infrastructure.

You should be familiar with using certificates and setting up client authentication for your servlet container before attempting to use it with Acegi Security. Most of the work is in creating and installing suitable certificates and keys. For example, if you're using Tomcat then read the instructions here http://jakarta.apache.org/tomcat/tomcat-5.0-doc/ssl-howto.html. It's important that you get this working before trying it out with Acegi Security.

### 1.13.2. X509 with Acegi Security

With X509 authentication, there is no explicit login procedure so the implementation is relatively simple; there is no need to redirect requests in order to interact with the user. As a result, some of the classes behave slightly differently from their equivalents in other packages. For example, the default “entry point” class, which is normally responsible for starting the authentication process, is only invoked if the certificate is rejected and it always returns an error to the user. With a suitable bean configuration, the normal sequence of events is as follows

1. The `X509ProcessingFilter` extracts the certificate from the request and uses it as the credentials for an authentication request. The generated authentication request is an `X509AuthenticationToken`. The request is passed to the authentication manager.

2. The `X509AuthenticationProvider` receives the token. Its main concern is to obtain the user information (in particular the user's granted authorities) that matches the certificate. It delegates this responsibility to an `X509AuthoritiesPopulator`.

3. The populator's single method, `getUserDetails(X509Certificate userCertificate)` is invoked. Implementations should return a `UserDetails` instance containing the array of `GrantedAuthority` objects for the user. This method can also choose to reject the certificate (for example if it doesn't contain a matching user name). In such cases it should throw a `BadCredentialsException`. A DAO-based implementation, `DaoX509AuthoritiesPopulator`, is provided which extracts the user's name from the subject “common name” (CN) in the certificate. It also allows you to set your own regular expression to match a different part of the subject's distinguished name. A UserDetailsService is used to load the user information.

4. If everything has gone smoothly then there should be a valid `Authentication` object in the secure context and the invocation will procede as normal. If no certificate was found, or the certificate was rejected, then the `SecurityEnforcementFilter` will invoke the `X509ProcessingFilterEntryPoint` which returns a 403 error (forbidden) to the user.

### 1.13.3. Configuring the X509 Provider

There is a version of the Contacts Sample Application which uses X509. Copy the beans and filter setup from this as a starting point for configuring your own application. A set of example certificates is also included which you can use to configure your server. These are

- `marissa.p12`: A PKCS12 format file containing the client key and certificate. These should be installed in your browser. It maps to the user “marissa” in the application.

- `server.p12`: The server certificate and key for HTTPS connections.

- `ca.jks`: A Java keystore containing the certificate for the authority which issued marissa's certificate. This will be used by the container to validate client certificates.

For JBoss 3.2.7 (with Tomcat 5.0), the SSL configuration in the `server.xml` file looks like this

    <!-- SSL/TLS Connector configuration -->
    <Connector port="8443" address="${jboss.bind.address}"
      maxThreads="100" minSpareThreads="5" maxSpareThreads="15"
      scheme="https" secure="true"
      sslProtocol = "TLS"
      clientAuth="true" keystoreFile="${jboss.server.home.dir}/conf/server.p12"
      keystoreType="PKCS12" keystorePass="password"
      truststoreFile="${jboss.server.home.dir}/conf/ca.jks"
      truststoreType="JKS" truststorePass="password"
    />

`clientAuth` can also be set to `want` if you still want SSL connections to succeed even if the client doesn't provide a certificate. Obviously these clients won't be able to access any objects secured by Acegi Security (unless you use a non-X509 authentication mechanism, such as BASIC authentication, to authenticate the user).

## 1.14. Channel Security

### 1.14.1. Overview

In addition to coordinating the authentication and authorization requirements of your application, the Acegi Security System for Spring is also able to ensure unauthenticated web requests have certain properties. These properties may include being of a particular transport type, having a particular `HttpSession` attribute set and so on. The most common requirement is for your web requests to be received using a particular transport protocol, such as HTTPS.

An important issue in considering transport security is that of session hijacking. Your web container manages a `HttpSession` by reference to a `jsessionid` that is sent to user agents either via a cookie or URL rewriting. If the `jsessionid` is ever sent over HTTP, there is a possibility that session identifier can be intercepted and used to impersonate the user after they complete the authentication process. This is because most web containers maintain the same session identifier for a given user, even after they switch from HTTP to HTTPS pages.

If session hijacking is considered too significant a risk for your particular application, the only option is to use HTTPS for every request. This means the `jsessionid` is never sent across an insecure channel. You will need to ensure your `web.xml`-defined `<welcome-file>` points to a HTTPS location, and the application never directs the user to a HTTP location. The Acegi Security System for Spring provides a solution to assist with the latter.

### 1.14.2. Configuration

To utilise Acegi Security's channel security services, add the following lines to `web.xml`:

    <filter>
      <filter-name>Acegi Channel Processing Filter</filter-name>
      <filter-class>org.acegisecurity.util.FilterToBeanProxy</filter-class>
      <init-param>
        <param-name>targetClass</param-name>
        <param-value>org.acegisecurity.securechannel.ChannelProcessingFilter</param-value>
      </init-param>
    </filter>

    <filter-mapping>
      <filter-name>Acegi Channel Processing Filter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

As usual when running `FilterToBeanProxy`, you will also need to configure the filter in your application context:

    <bean id="channelProcessingFilter" class="org.acegisecurity.securechannel.ChannelProcessingFilter">
      <property name="channelDecisionManager"><ref bean="channelDecisionManager"/></property>
      <property name="filterInvocationDefinitionSource">
        <value>
          CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
          \A/secure/.*\Z=REQUIRES_SECURE_CHANNEL
          \A/acegilogin.jsp.*\Z=REQUIRES_SECURE_CHANNEL
          \A/j_acegi_security_check.*\Z=REQUIRES_SECURE_CHANNEL
          \A.*\Z=REQUIRES_INSECURE_CHANNEL
        </value>
      </property>
    </bean>

    <bean id="channelDecisionManager" class="org.acegisecurity.securechannel.ChannelDecisionManagerImpl">
      <property name="channelProcessors">
        <list>
          <ref bean="secureChannelProcessor"/>
          <ref bean="insecureChannelProcessor"/>
        </list>
      </property>
    </bean>

    <bean id="secureChannelProcessor" class="org.acegisecurity.securechannel.SecureChannelProcessor"/>
    <bean id="insecureChannelProcessor" class="org.acegisecurity.securechannel.InsecureChannelProcessor"/>

Like `FilterSecurityInterceptor`, Apache Ant style paths are also supported by the `ChannelProcessingFilter`.

The `ChannelProcessingFilter` operates by filtering all web requests and determining the configuration attributes that apply. It then delegates to the `ChannelDecisionManager`. The default implementation, `ChannelDecisionManagerImpl`, should suffice in most cases. It simply delegates through the list of configured `ChannelProcessor` instances. A `ChannelProcessor` will review the request, and if it is unhappy with the request (eg it was received across the incorrect transport protocol), it will perform a redirect, throw an exception or take whatever other action is appropriate.

Included with the Acegi Security System for Spring are two concrete `ChannelProcessor` implementations: `SecureChannelProcessor` ensures requests with a configuration attribute of `REQUIRES_SECURE_CHANNEL` are received over HTTPS, whilst `InsecureChannelProcessor` ensures requests with a configuration attribute of `REQUIRES_INSECURE_CHANNEL` are received over HTTP. Both implementations delegate to a `ChannelEntryPoint` if the required transport protocol is not used. The two `ChannelEntryPoint` implementations included with Acegi Security simply redirect the request to HTTP and HTTPS as appropriate. Appropriate defaults are assigned to the `ChannelProcessor` implementations for the configuration attribute keywords they respond to and the `ChannelEntryPoint` they delegate to, although you have the ability to override these using the application context.

Note that the redirections are absolute (eg `http://www.company.com:8080/app/page`), not relative (eg `/app/page`). During testing it was discovered that Internet Explorer 6 Service Pack 1 has a bug whereby it does not respond correctly to a redirection instruction which also changes the port to use. Accordingly, absolute URLs are used in conjunction with bug detection logic in the `PortResolverImpl` that is wired up by default to many Acegi Security beans. Please refer to the JavaDocs for `PortResolverImpl` for further details.

### 1.14.3. Usage

Once configured, using the channel security filter is very easy. Simply request pages without regard to the protocol (ie HTTP or HTTPS) or port (eg 80, 8080, 443, 8443 etc). Obviously you'll still need a way of making the initial request (probably via the `web.xml` `<welcome-file>` or a well-known home page URL), but once this is done the filter will perform redirects as defined by your application context.

You can also add your own `ChannelProcessor` implementations to the `ChannelDecisionManagerImpl`. For example, you might set a `HttpSession` attribute when a human user is detected via a "enter the contents of this graphic" procedure. Your `ChannelProcessor` would respond to say `REQUIRES_HUMAN_USER` configuration attributes and redirect to an appropriate entry point to start the human user validation process if the `HttpSession` attribute is not currently set.

To decide whether a security check belongs in a `ChannelProcessor` or an `AccessDecisionVoter`, remember that the former is designed to handle unauthenticated requests, whilst the latter is designed to handle authenticated requests. The latter therefore has access to the granted authorities of the authenticated principal. In addition, problems detected by a `ChannelProcessor` will generally cause a HTTP/HTTPS redirection so its requirements can be met, whilst problems detected by an `AccessDecisionVoter` will ultimately result in an `AccessDeniedException` (depending on the governing `AccessDecisionManager`).

## 1.15. Instance-Based Access Control List (ACL) Security

### 1.15.1. Overview

Complex applications often will find the need to define access permissions not simply at a web request or method invocation level. Instead, security decisions need to comprise both who (`Authentication`), where (`MethodInvocation`) and what (`SomeDomainObject`). In other words, authorization decisions also need to consider the actual domain object instance subject of a method invocation.

Imagine you're designing an application for a pet clinic. There will be two main groups of users of your Spring-based application: staff of the pet clinic, as well as the pet clinic's customers. The staff will have access to all of the data, whilst your customers will only be able to see their own customer records. To make it a little more interesting, your customers can allow other users to see their customer records, such as their "puppy preschool "mentor or president of their local "Pony Club". Using Acegi Security System for Spring as the foundation, you have several approaches that can be used:

1. Write your business methods to enforce the security. You could consult a collection within the `Customer` domain object instance to determine which users have access. By using the `SecurityContextHolder.getContext().getAuthentication()`, you'll be able to access the `Authentication` object.

2. Write an `AccessDecisionVoter` to enforce the security from the `GrantedAuthority[]`s stored in the `Authentication` object. This would mean your `AuthenticationManager` would need to populate the `Authentication` with custom `GrantedAuthority`[]s representing each of the `Customer` domain object instances the principal has access to.

3. Write an `AccessDecisionVoter` to enforce the security and open the target `Customer` domain object directly. This would mean your voter needs access to a DAO that allows it to retrieve the `Customer` object. It would then access the `Customer` object's collection of approved users and make the appropriate decision.

Each one of these approaches is perfectly legitimate. However, the first couples your authorization checking to your business code. The main problems with this include the enhanced difficulty of unit testing and the fact it would be more difficult to reuse the `Customer` authorization logic elsewhere. Obtaining the `GrantedAuthority[]`s from the `Authentication` object is also fine, but will not scale to large numbers of `Customer`s. If a user might be able to access 5,000 `Customer`s (unlikely in this case, but imagine if it were a popular vet for a large Pony Club!) the amount of memory consumed and time required to construct the `Authentication` object would be undesirable. The final method, opening the `Customer` directly from external code, is probably the best of the three. It achieves separation of concerns, and doesn't misuse memory or CPU cycles, but it is still inefficient in that both the `AccessDecisionVoter` and the eventual business method itself will perform a call to the DAO responsible for retrieving the `Customer` object. Two accesses per method invocation is clearly undesirable. In addition, with every approach listed you'll need to write your own access control list (ACL) persistence and business logic from scratch.

Fortunately, there is another alternative, which we'll talk about below.

### 1.15.2. The org.acegisecurity.acl Package

The `org.acegisecurity.acl` package is very simple, comprising only a handful of interfaces and a single class, as shown in Figure 6. It provides the basic foundation for access control list (ACL) lookups.

Figure 6: Access Control List Manager

The central interface is `AclManager`, which is defined by two methods:

    public AclEntry[] getAcls(java.lang.Object domainInstance);
    public AclEntry[] getAcls(java.lang.Object domainInstance, Authentication authentication);

`AclManager` is intended to be used as a collaborator against your business objects, or, more desirably, `AccessDecisionVoter`s. This means you use Spring's normal `ApplicationContext` features to wire up your `AccessDecisionVoter` (or business method) with an `AclManager`. Consideration was given to placing the ACL information in the `ContextHolder`, but it was felt this would be inefficient both in terms of memory usage as well as the time spent loading potentially unused ACL information. The trade-off of needing to wire up a collaborator for those objects requiring ACL information is rather minor, particularly in a Spring-managed application.

The first method of the `AclManager` will return all ACLs applying to the domain object instance passed to it. The second method does the same, but only returns those ACLs which apply to the passed `Authentication` object.

The `AclEntry` interface returned by `AclManager` is merely a marker interface. You will need to provide an implementation that reflects that ACL permissions for your application.

Rounding out the `org.acegisecurity.acl` package is an `AclProviderManager` class, with a corresponding `AclProvider` interface. `AclProviderManager` is a concrete implementation of `AclManager`, which iterates through registered `AclProvider`s. The first `AclProvider` that indicates it can authoritatively provide ACL information for the presented domain object instance will be used. This is very similar to the `AuthenticationProvider` interface used for authentication.

With this background, let's now look at a usable ACL implementation.

### 1.15.3. Integer Masked ACLs

Acegi Security System for Spring includes a production-quality ACL provider implementation, which is shown in Figure 7.

Figure 7: Basic ACL Manager

The implementation is based on integer masking, which is commonly used for ACL permissions given its flexibility and speed. Anyone who has used Unix's `chmod` command will know all about this type of permission masking (eg `chmod 777`). You'll find the classes and interfaces for the integer masking ACL package under `org.acegisecurity.acl.basic`.

Extending the `AclEntry` interface is a `BasicAclEntry` interface, with the main methods shown below:

    public AclObjectIdentity getAclObjectIdentity();
    public AclObjectIdentity getAclObjectParentIdentity();
    public int getMask();
    public java.lang.Object getRecipient();

As shown, each `BasicAclEntry` has four main properties. The `mask` is the integer that represents the permissions granted to the `recipient`. The `aclObjectIdentity` is able to identify the domain object instance for which the ACL applies, and the `aclObjectParentIdentity` optionally specifies the parent of the domain object instance. Multiple `BasicAclEntry`s usually exist against a single domain object instance, and as suggested by the parent identity property, permissions granted higher in the object hierarchy will trickle down and be inherited (unless blocked by integer zero).

`BasicAclEntry` implementations typically provide convenience methods, such as `isReadAllowed()`, to avoid application classes needing to perform bit masking themselves. The `SimpleAclEntry` and `AbstractBasicAclEntry` demonstrate and provide much of this bit masking logic.

The `AclObjectIdentity` itself is merely a marker interface, so you need to provide implementations for your domain objects. However, the package does include a `NamedEntityObjectIdentity` implementation which will suit many needs. The `NamedEntityObjectIdentity` identifies a given domain object instance by the classname of the instance and the identity of the instance. A `NamedEntityObjectIdentity` can be constructed manually (by calling the constructor and providing the classname and identity `String`s), or by passing in any domain object that contains a `getId()` method.

The actual `AclProvider` implementation is named `BasicAclProvider`. It has adopted a similar design to that used by the authentication-related `DaoAuthenticationProvder`. Specifically, you define a `BasicAclDao` against the provider, so different ACL repository types can be accessed in a pluggable manner. The `BasicAclProvider` also supports pluggable cache providers (with Acegi Security System for Spring including an implementation that fronts EH-CACHE).

The `BasicAclDao` interface is very simple to implement:

    public BasicAclEntry[] getAcls(AclObjectIdentity aclObjectIdentity);

A `BasicAclDao` implementation needs to understand the presented `AclObjectIdentity` and how it maps to a storage repository, find the relevant records, and create appropriate `BasicAclEntry` objects and return them.

Acegi Security includes a single `BasicAclDao` implementation called `JdbcDaoImpl`. As implied by the name, `JdbcDaoImpl` accesses ACL information from a JDBC database. There is also an extended version of this DAO, `JdbcExtendedDaoImpl`, which provides CRUD operations on the JDBC database, although we won't discuss these features here. The default database schema and some sample data will aid in understanding its function:

    CREATE TABLE acl_object_identity (
         id IDENTITY NOT NULL,
         object_identity VARCHAR_IGNORECASE(250) NOT NULL,
         parent_object INTEGER,
         acl_class VARCHAR_IGNORECASE(250) NOT NULL,
         CONSTRAINT unique_object_identity UNIQUE(object_identity),
         FOREIGN KEY (parent_object) REFERENCES acl_object_identity(id)
    );

    CREATE TABLE acl_permission (
         id IDENTITY NOT NULL,
         acl_object_identity INTEGER NOT NULL,
         recipient VARCHAR_IGNORECASE(100) NOT NULL,
         mask INTEGER NOT NULL,
         CONSTRAINT unique_recipient UNIQUE(acl_object_identity, recipient),
         FOREIGN KEY (acl_object_identity) REFERENCES acl_object_identity(id)
    );

    INSERT INTO acl_object_identity VALUES (1, 'corp.DomainObject:1', null, 'org.acegisecurity.acl.basic.SimpleAclEntry');
    INSERT INTO acl_object_identity VALUES (2, 'corp.DomainObject:2', 1, 'org.acegisecurity.acl.basic.SimpleAclEntry');
    INSERT INTO acl_object_identity VALUES (3, 'corp.DomainObject:3', 1, 'org.acegisecurity.acl.basic.SimpleAclEntry');
    INSERT INTO acl_object_identity VALUES (4, 'corp.DomainObject:4', 1, 'org.acegisecurity.acl.basic.SimpleAclEntry');
    INSERT INTO acl_object_identity VALUES (5, 'corp.DomainObject:5', 3, 'org.acegisecurity.acl.basic.SimpleAclEntry');
    INSERT INTO acl_object_identity VALUES (6, 'corp.DomainObject:6', 3, 'org.acegisecurity.acl.basic.SimpleAclEntry');

    INSERT INTO acl_permission VALUES (null, 1, 'ROLE_SUPERVISOR', 1);
    INSERT INTO acl_permission VALUES (null, 2, 'ROLE_SUPERVISOR', 0);
    INSERT INTO acl_permission VALUES (null, 2, 'marissa', 2);
    INSERT INTO acl_permission VALUES (null, 3, 'scott', 14);
    INSERT INTO acl_permission VALUES (null, 6, 'scott', 1);

As can be seen, database-specific constraints are used extensively to ensure the integrity of the ACL information. If you need to use a different database (Hypersonic SQL statements are shown above), you should try to implement equivalent constraints.

The `JdbcDaoImpl` will only respond to requests for `NamedEntityObjectIdentity`s. It converts such identities into a single `String`, comprising the`NamedEntityObjectIdentity.getClassname()` + `":"` + `NamedEntityObjectIdentity.getId()`. This yields the type of `object_identity` values shown above. As indicated by the sample data, each database row corresponds to a single `BasicAclEntry`. As stated earlier and demonstrated by `corp.DomainObject:2` in the above sample data, each domain object instance will often have multiple `BasicAclEntry`[]s.

As `JdbcDaoImpl` is required to return concrete `BasicAclEntry` classes, it needs to know which `BasicAclEntry` implementation it is to create and populate. This is the role of the `acl_class` column. `JdbcDaoImpl` will create the indicated class and set its `mask`, `recipient`, `aclObjectIdentity` and `aclObjectParentIdentity` properties.

As you can probably tell from the sample data, the `parent_object_identity` value can either be null or in the same format as the `object_identity`. If non-null, `JdbcDaoImpl` will create a `NamedEntityObjectIdentity` to place inside the returned `BasicAclEntry` class.

Returning to the `BasicAclProvider`, before it can poll the `BasicAclDao` implementation it needs to convert the domain object instance it was passed into an `AclObjectIdentity`. `BasicAclProvider` has a `protected AclObjectIdentity obtainIdentity(Object domainInstance)` method that is responsible for this. As a protected method, it enables subclasses to easily override. The normal implementation checks whether the passed domain object instance implements the `AclObjectIdentityAware` interface, which is merely a getter for an `AclObjectIdentity`. If the domain object does implement this interface, that is the identity returned. If the domain object does not implement this interface, the method will attempt to create an `AclObjectIdentity` by passing the domain object instance to the constructor of a class defined by the `BasicAclProvider.getDefaultAclObjectIdentity()` method. By default the defined class is `NamedEntityObjectIdentity`, which was described in more detail above. Therefore, you will need to either (i) provide a `getId()` method on your domain objects, (ii) implement `AclObjectIdentityAware` on your domain objects, (iii) provide an alternative `AclObjectIdentity` implementation that will accept your domain object in its constructor, or (iv) override the `obtainIdentity(Object)` method.

Once the `AclObjectIdentity` of the domain object instance is determined, the `BasicAclProvider` will poll the DAO to obtain its `BasicAclEntry`[]s. If any of the entries returned by the DAO indicate there is a parent, that parent will be polled, and the process will repeat until there is no further parent. The permissions assigned to a `recipient` closest to the domain object instance will always take priority and override any inherited permissions. From the sample data above, the following inherited permissions would apply:

    --- Mask integer 0  = no permissions
    --- Mask integer 1  = administer
    --- Mask integer 2  = read
    --- Mask integer 6  = read and write permissions
    --- Mask integer 14 = read and write and create permissions

    ---------------------------------------------------------------------
    --- *** INHERITED RIGHTS FOR DIFFERENT INSTANCES AND RECIPIENTS ***
    --- INSTANCE  RECIPIENT         PERMISSION(S) (COMMENT #INSTANCE)
    ---------------------------------------------------------------------
    ---    1      ROLE_SUPERVISOR   Administer
    ---    2      ROLE_SUPERVISOR   None (overrides parent #1)
    ---           marissa           Read
    ---    3      ROLE_SUPERVISOR   Administer (from parent #1)
    ---           scott             Read, Write, Create
    ---    4      ROLE_SUPERVISOR   Administer (from parent #1)
    ---    5      ROLE_SUPERVISOR   Administer (from parent #3)
    ---           scott             Read, Write, Create (from parent #3)
    ---    6      ROLE_SUPERVISOR   Administer (from parent #3)
    ---           scott             Administer (overrides parent #3)

So the above explains how a domain object instance has its `AclObjectIdentity` discovered, and the `BasicAclDao` will be polled successively until an array of inherited permissions is constructed for the domain object instance. The final step is to determine the `BasicAclEntry`[]s that are actually applicable to a given `Authentication` object.

As you would recall, the `AclManager` (and all delegates, up to and including `BasicAclProvider`) provides a method which returns only those `BasicAclEntry`[]s applying to a passed `Authentication` object. `BasicAclProvider` delivers this functionality by delegating the filtering operation to an `EffectiveAclsResolver` implementation. The default implementation, `GrantedAuthorityEffectiveAclsResolver`, will iterate through the `BasicAclEntry`[]s and include only those where the `recipient` is equal to either the `Authentication`'s `principal` or any of the `Authentication`'s `GrantedAuthority`[]s. Please refer to the JavaDocs for more information.

Figure 8: ACL Instantiation Approach

### 1.15.4. Conclusion

Acegi Security's instance-specific ACL packages shield you from much of the complexity of developing your own ACL approach. The interfaces and classes detailed above provide a scalable, customisable ACL solution that is decoupled from your application code. Whilst the reference documentation may suggest complexity, the basic implementation is able to support most typical applications out-of-the-box.

## 1.16. Filters

### 1.16.1. Overview

The Acegi Security System for Spring uses filters extensively. Each filter is covered in detail in a respective section of this document. This section includes information that applies to all filters.

### 1.16.2. FilterToBeanProxy

Most filters are configured using the `FilterToBeanProxy`. An example configuration from `web.xml` follows:

    <filter>
      <filter-name>Acegi HTTP Request Security Filter</filter-name>
      <filter-class>org.acegisecurity.util.FilterToBeanProxy</filter-class>
      <init-param>
        <param-name>targetClass</param-name>
        <param-value>org.acegisecurity.ClassThatImplementsFilter</param-value>
      </init-param>
    </filter>

Notice that the filter in `web.xml` is actually a `FilterToBeanProxy`, and not the filter that will actually implements the logic of the filter. What `FilterToBeanProxy` does is delegate the `Filter`'s methods through to a bean which is obtained from the Spring application context. This enables the bean to benefit from the Spring application context lifecycle support and configuration flexibility. The bean must implement `javax.servlet.Filter`.

The `FilterToBeanProxy` only requires a single initialization parameter, `targetClass` or `targetBean`. The `targetClass` parameter locates the first object in the application context of the specified class, whilst `targetBean` locates the object by bean name. Like standard Spring web applications, the `FilterToBeanProxy` accesses the application context via`WebApplicationContextUtils.getWebApplicationContext(ServletContext)`, so you should configure a `ContextLoaderListener` in `web.xml`.

There is a lifecycle issue to consider when hosting `Filter`s in an IoC container instead of a servlet container. Specifically, which container should be responsible for calling the `Filter`'s "startup" and "shutdown" methods? It is noted that the order of initialization and destruction of a `Filter` can vary by servlet container, and this can cause problems if one `Filter` depends on configuration settings established by an earlier initialized `Filter`. The Spring IoC container on the other hand has more comprehensive lifecycle/IoC interfaces (such as `InitializingBean`, `DisposableBean`, `BeanNameAware`, `ApplicationContextAware` and many others) as well as a well-understood interface contract, predictable method invocation ordering, autowiring support, and even options to avoid implementing Spring interfaces (eg the `destroy-method` attribute in Spring XML). For this reason we recommend the use of Spring lifecycle services instead of servlet container lifecycle services wherever possible. By default `FilterToBeanProxy` will not delegate `init(FilterConfig)` and `destroy()` methods through to the proxied bean. If you do require such invocations to be delegated, set the `lifecycle` initialization parameter to `servlet-container-managed`.

### 1.16.3. FilterChainProxy

We strongly recommend to use `FilterChainProxy` instead of adding multiple filters to `web.xml`.

Whilst `FilterToBeanProxy` is a very useful class, the problem is that the lines of code required for `<filter>` and `<filter-mapping>` entries in `web.xml` explodes when using more than a few filters. To overcome this issue, Acegi Security provides a `FilterChainProxy` class. It is wired using a `FilterToBeanProxy` (just like in the example above), but the target class is `org.acegisecurity.util.FilterChainProxy`. The filter chain is then declared in the application context, using code such as this:

    <bean id="filterChainProxy" class="org.acegisecurity.util.FilterChainProxy">
      <property name="filterInvocationDefinitionSource">
        <value>
          CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
          PATTERN_TYPE_APACHE_ANT
          /webServices/**=httpSessionContextIntegrationFilterWithASCFalse,basicProcessingFilter,securityEnforcementFilter
          /**=httpSessionContextIntegrationFilterWithASCTrue,authenticationProcessingFilter,securityEnforcementFilter
        </value>
      </property>
    </bean>

You may notice similarities with the way `SecurityEnforcementFilter` is declared. Both regular expressions and Ant Paths are supported, and the most specific URIs appear first. At runtime the `FilterChainProxy` will locate the first URI pattern that matches the current web request. Each of the corresponding configuration attributes represent the name of a bean defined in the application context. The filters will then be invoked in the order they are specified, with standard `FilterChain` behaviour being respected (a `Filter` can elect not to proceed with the chain if it wishes to end processing).

As you can see, `FitlerChainProxy` requires the duplication of filter names for different request patterns (in the above example, `httpSessionContextIntegrationFilter` and `securityEnforcementFilter` are duplicated). This design decision was made to enable `FilterChainProxy` to specify different `Filter` invocation orders for different URI patterns, and also to improve both the expressiveness (in terms of regular expressions, Ant Paths, and any custom `FilterInvocationDefinitionSource` implementations) and clarity of which `Filter`s should be invoked.

You may have noticed we have declared two `HttpSessionContextIntegrationFilter`s in the filter chain (`ASC` is short for `allowSessionCreation`, a property of `HttpSessionContextIntegrationFilter`). As web services will never present a `jsessionid` on future requests, creating `HttpSession`s for such user agents would be wasteful. If you had a high-volume application which required maximum scalability, we recommend you use the approach shown above. For smaller applications, using a single `HttpSessionContextIntegrationFilter` (with its default `allowSessionCreation` as `true`) would likely be sufficient.

In relation to lifecycle issues, the `FilterChainProxy` will always delegate `init(FilterConfig)` and `destroy()` methods through to the underlaying `Filter`s if such methods are called against `FilterChainProxy` itself. In this case, `FilterChainProxy` guarantees to only initialize and destroy each `Filter` once, irrespective of how many times it is declared by the `FilterInvocationDefinitionSource`. You control the overall choice as to whether these methods are called or not via the `lifecycle` initialization parameter of the `FilterToBeanProxy` that proxies `FilterChainProxy`. As discussed above, by default any servlet container lifecycle invocations are not delegated through to `FilterChainProxy`.

### 1.16.4. Filter Ordering

The order that filters are defined in `web.xml` is important. NB: THE FILTER ORDER CHANGED FROM VERSION 0.8.0.

Irrespective of which filters you are actually using, the order of the `<filter-mapping>`s should be as follows:

1. `ChannelProcessingFilter`, because it might need to redirect to a different protocol

2. `ConcurrentSessionFilter`, because it doesn't use any `SecurityContextHolder` functionality but needs to update the `SessionRegistry` to reflect ongoing requests from the principal

3. `HttpSessionContextIntegrationFilter`, so a `Context` can be setup in the `SecurityContextHolder` at the beginning of a web request, and any changes to the Context can be copied to the `HttpSession` when the web request ends (ready for use with the next web request)

4. Authentication processing mechanisms - `AuthenticationProcessingFilter`, `CasProcessingFilter`, `BasicProcessingFilter, HttpRequestIntegrationFilter, JbossIntegrationFilter` etc - so that the `SecurityContextHolder` can be modified to contain a valid `Authentication` request token

5. The `ContextHolderAwareRequestFilter`, if you are using it to install an Acegi Security aware `HttpServletRequestWrapper` into your servlet container

6. `RememberMeProcessingFilter`, so that if no earlier authentication processing mechanism updated the `SecurityContextHolder`, and the request presents a cookie that enables remember-me services to take place, a suitable remembered ``Authentication`` object will be put there

7. `AnonymousProcessingFilter`, so that if no earlier authentication processing mechanism updated the `SecurityContextHolder`, an anonymous `Authentication` object will be put there

8. `SecurityEnforcementFilter`, to protect web URIs and catch any Acegi Security exceptions so that an appropriate `AuthenticationEntryPoint` can be launched

All of the above filters use `FilterToBeanProxy` or `FilterChainProxy`, which is discussed in the previous sections. It is recommended that a single `FilterToBeanProxy` proxy through to a single `FilterChainProxy` for each application, with that `FilterChainProxy` defining all of the Acegi Security `Filter`s.

If you're using SiteMesh, ensure the Acegi Security filters execute before the SiteMesh filters are called. This enables the `SecurityContextHolder` to be populated in time for use by SiteMesh decorators.

## 1.17. Contacts Sample Application

Included with the Acegi Security System for Spring is a very simple application that can demonstrate the basic security facilities provided by the system (and confirm your Container Adapter is properly configured if you're using one).

If you build from CVS, the Contacts sample application includes three deployable versions: `acegi-security-sample-contacts-filter.war` is configured with the HTTP Session Authentication approach. The ``acegi-security-sample-contacts-ca.war`` is configured to use a Container Adapter. Finally, `acegi-security-sample-contacts-cas.war` is designed to work with a Yale CAS server. If you're just wanting to see how the sample application works, please use ``acegi-security-sample-contacts-filter.war`` as it does not require special configuration of your container. This is also the artifact included in ofiical release ZIPs.

To deploy, simply copy the relevant WAR file from the Acegi Security System for Spring distribution into your container’s `webapps` directory.

After starting your container, check the application can load. Visit `http://localhost:```8080/`acegi-security-sample-contacts-filter` (or whichever URL is appropriate for your web container and the WAR you deployed). A random contact should be displayed. Click "Refresh" several times and you will see different contacts. The business method that provides this random contact is not secured.

Next, click "Debug". You will be prompted to authenticate, and a series of usernames and passwords are suggested on that page. Simply authenticate with any of these and view the resulting page. It should contain a success message similar to the following:

> Context on SecurityContextHolder is of type: org.acegisecurity.context.SecurityContextImpl

> The Context implements SecurityContext.

> Authentication object is of type: org.acegisecurity.adapters.PrincipalAcegiUserToken

> Authentication object as a String: org.acegisecurity.adapters.PrincipalAcegiUserToken@e9a7c2: Username: marissa; Password: [PROTECTED]; Authenticated: true; Granted Authorities: ROLE_TELLER, ROLE_SUPERVISOR

> Authentication object holds the following granted authorities:

> ROLE_TELLER (getAuthority(): ROLE_TELLER)

> ROLE_SUPERVISOR (getAuthority(): ROLE_SUPERVISOR)

> SUCCESS! Your [container adapter|web filter] appears to be properly configured!

If you receive a different message, and deployed `acegi-security-sample-contacts-ca.war`, check you have properly configured your Container Adapter as described elsewhere in this reference guide.

Once you successfully receive the above message, return to the sample application's home page and click "Manage". You can then try out the application. Notice that only the contacts available to the currently logged on user are displayed, and only users with `ROLE_SUPERVISOR` are granted access to delete their contacts. Behind the scenes, the `MethodSecurityInterceptor` is securing the business objects. If you're using ``acegi-security-sample-contacts-filter.war`` or `acegi-security-sample-contacts-cas.war`, the `FilterSecurityInterceptor` is also securing the HTTP requests. If using either of these WARs, be sure to try visiting `http://localhost:8080/contacts/secure/super`, which will demonstrate access being denied by the `SecurityEnforcementFilter`. Note the sample application enables you to modify the access control lists associated with different contacts. Be sure to give this a try and understand how it works by reviewing the sample application's application context XML files.

The Contacts sample application also include a `client` directory. Inside you will find a small application that queries the backend business objects using several web services protocols. This demonstrates how to use the Acegi Security System for Spring for authentication with Spring remoting protocols. To try this client, ensure your servlet container is still running the Contacts sample application, and then execute `client marissa koala`. The command-line parameters respectively represent the username to use, and the password to use. Note that you may need to edit `client.properties` to use a different target URL.

Please note the sample application's `client` does not currently support CAS. You can still give it a try, though, if you're ambitious: try `client _cas_stateless_ YOUR-SERVICE-TICKET-ID`.

## 1.18. Become Involved

We welcome you to become involved in the Acegi Security System for Spring project. There are many ways of contributing, including reading the mailing list and responding to questions from other people, writing new code, improving existing code, assisting with documentation, or simply making suggestions. Please read our project policies web page that is available on the Acegi Security home page. This explains the path to become a committer, and the administration approaches we use with the project.

SourceForge provides CVS services for the project, allowing anybody to access the latest code. If you wish to contribute new code, please observe the following requirements. These exist to maintain the quality and consistency of the project:

- Use a suitable IDE Jalopy plug-in to convert your code into the project's consistent style

- Ensure your code does not break any unit tests (run the Maven `test:test` goal)

- If you have added new code, please provide suitable unit tests (use the Maven `clover:html-report` to view coverage)

- Join the acegisecurity-developer and acegisecurity-cvs mailing lists so you're in the loop

- Use CamelCase

- Add code contributions to JIRA

- Add a CVS `$Id: index.xml,v 1.3 2004/04/02 21:12:25 fbos Exp $` tag to the JavaDocs for any new class you create

## 1.19. Further Information

Questions and comments on the Acegi Security System for Spring are welcome. Please use the Spring Community Forum web site at `http://forum.springframework.org`. You're also welcome to join the acegisecurity-developer mailing list. Our project home page (where you can obtain the latest release of the project and access to CVS, mailing lists, forums etc) is at `http://acegisecurity.sourceforge.net`.