/* Copyright 2004, 2005 Acegi Technology Pty Limited
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.acegisecurity.ui.digestauth;
  
  import org.acegisecurity.AuthenticationException;
  import org.acegisecurity.intercept.web.AuthenticationEntryPoint;
  
  import org.apache.commons.codec.binary.Base64;
  import org.apache.commons.codec.digest.DigestUtils;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import org.springframework.beans.factory.InitializingBean;
  
  import java.io.IOException;
  
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletResponse;
  
  
  /***
   * Used by the <code>SecurityEnforcementFilter</code> to commence
   * authentication via the {@link DigestProcessingFilter}.
   * 
   * <p>
   * The nonce sent back to the user agent will be valid for the period indicated
   * by {@link #setNonceValiditySeconds(int)}. By default this is 300 seconds.
   * Shorter times should be used if replay attacks are a major concern. Larger
   * values can be used if performance is a greater concern. This class
   * correctly presents the <code>stale=true</code> header when the nonce has
   * expierd, so properly implemented user agents will automatically renegotiate
   * with a new nonce value (ie without presenting a new password dialog box to
   * the user).
   * </p>
   *
   * @author Ben Alex
   * @version $Id: DigestProcessingFilterEntryPoint.java,v 1.2 2005/11/17 00:56:10 benalex Exp $
   */
  public class DigestProcessingFilterEntryPoint
      implements AuthenticationEntryPoint, InitializingBean {
      //~ Static fields/initializers =============================================
  
      private static final Log logger = LogFactory.getLog(DigestProcessingFilterEntryPoint.class);
  
      //~ Instance fields ========================================================
  
      private String key;
      private String realmName;
      private int nonceValiditySeconds = 300;
  
      //~ Methods ================================================================
  
      public void setKey(String key) {
          this.key = key;
      }
  
      public String getKey() {
          return key;
      }
  
      public void setNonceValiditySeconds(int nonceValiditySeconds) {
          this.nonceValiditySeconds = nonceValiditySeconds;
      }
  
      public int getNonceValiditySeconds() {
          return nonceValiditySeconds;
      }
  
      public void setRealmName(String realmName) {
          this.realmName = realmName;
      }
  
      public String getRealmName() {
          return realmName;
      }
  
      public void afterPropertiesSet() throws Exception {
          if ((realmName == null) || "".equals(realmName)) {
              throw new IllegalArgumentException("realmName must be specified");
          }
  
          if ((key == null) || "".equals(key)) {
              throw new IllegalArgumentException("key must be specified");
          }
     }
 
     public void commence(ServletRequest request, ServletResponse response,
         AuthenticationException authException)
         throws IOException, ServletException {
         HttpServletResponse httpResponse = (HttpServletResponse) response;
 
         // compute a nonce (do not use remote IP address due to proxy farms)
         // format of nonce is:  
         //   base64(expirationTime + ":" + md5Hex(expirationTime + ":" + key))
         long expiryTime = System.currentTimeMillis()
             + (nonceValiditySeconds * 1000);
         String signatureValue = new String(DigestUtils.md5Hex(expiryTime + ":"
                     + key));
         String nonceValue = expiryTime + ":" + signatureValue;
         String nonceValueBase64 = new String(Base64.encodeBase64(
                     nonceValue.getBytes()));
 
         // qop is quality of protection, as defined by RFC 2617.
         // we do not use opaque due to IE violation of RFC 2617 in not
         // representing opaque on subsequent requests in same session.
         String authenticateHeader = "Digest realm=\"" + realmName + "\", "
             + "qop=\"auth\", nonce=\"" + nonceValueBase64 + "\"";
 
         if (authException instanceof NonceExpiredException) {
             authenticateHeader = authenticateHeader + ", stale=\"true\"";
         }
 
         if (logger.isDebugEnabled()) {
             logger.debug("WWW-Authenticate header sent to user agent: "
                 + authenticateHeader);
         }
 
         httpResponse.addHeader("WWW-Authenticate", authenticateHeader);
         httpResponse.sendError(HttpServletResponse.SC_UNAUTHORIZED,
             authException.getMessage());
     }
 }