/**
  * Generate the challenge string.
  *
  * @return a generated nonce.
  */
 public String generateNonce() {
   // Get the time of day and run MD5 over it.
   Date date = new Date();
   long time = date.getTime();
   Random rand = new Random();
   long pad = rand.nextLong();
   String nonceString = (new Long(time)).toString() + (new Long(pad)).toString();
   byte mdbytes[] = messageDigest.digest(nonceString.getBytes());
   // Convert the mdbytes array into a hex string.
   return ProxyUtilities.toHexString(mdbytes);
 }
  /**
   * Check the response and answer true if authentication succeeds. We are making simplifying
   * assumptions here and assuming that the password is available to us for computation of the MD5
   * hash. We also dont cache authentications so that the user has to authenticate on each
   * registration.
   *
   * @param user is the username
   * @param authHeader is the Authroization header from the SIP request.
   * @param requestLine is the SIP Request line from the SIP request.
   * @exception SIPAuthenticationException is thrown when authentication fails or message is bad
   */
  public boolean doAuthenticate(String user, AuthorizationHeader authHeader, Request request) {
    String realm = authHeader.getRealm();
    String username = authHeader.getUsername();
    URI requestURI = request.getRequestURI();

    if (username == null) {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
              + "WARNING: userName parameter not set in the header received!!!");
      username = user;
    }
    if (realm == null) {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
              + "WARNING: realm parameter not set in the header received!!! WE use the default one");
      realm = DEFAULT_REALM;
    }

    ProxyDebug.println(
        "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
            + "Trying to authenticate user: "******" for "
            + " the realm: "
            + realm);

    String password = (String) passwordTable.get(username + "@" + realm);
    if (password == null) {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
              + "ERROR: password not found for the user: "******"@"
              + realm);
      return false;
    }

    String nonce = authHeader.getNonce();
    // If there is a URI parameter in the Authorization header,
    // then use it.
    URI uri = authHeader.getURI();
    // There must be a URI parameter in the authorization header.
    if (uri == null) {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
              + "ERROR: uri paramater not set in the header received!");
      return false;
    }

    ProxyDebug.println(
        "DEBUG, DigestAuthenticationMethod, doAuthenticate(), username:"******"!");
    ProxyDebug.println("DEBUG, DigestAuthenticationMethod, doAuthenticate(), realm:" + realm + "!");
    ProxyDebug.println(
        "DEBUG, DigestAuthenticationMethod, doAuthenticate(), password:"******"!");
    ProxyDebug.println("DEBUG, DigestAuthenticationMethod, doAuthenticate(), uri:" + uri + "!");
    ProxyDebug.println("DEBUG, DigestAuthenticationMethod, doAuthenticate(), nonce:" + nonce + "!");
    ProxyDebug.println(
        "DEBUG, DigestAuthenticationMethod, doAuthenticate(), method:" + request.getMethod() + "!");

    String A1 = username + ":" + realm + ":" + password;
    String A2 = request.getMethod().toUpperCase() + ":" + uri.toString();
    byte mdbytes[] = messageDigest.digest(A1.getBytes());
    String HA1 = ProxyUtilities.toHexString(mdbytes);

    ProxyDebug.println("DEBUG, DigestAuthenticationMethod, doAuthenticate(), HA1:" + HA1 + "!");
    mdbytes = messageDigest.digest(A2.getBytes());
    String HA2 = ProxyUtilities.toHexString(mdbytes);
    ProxyDebug.println("DEBUG, DigestAuthenticationMethod, doAuthenticate(), HA2:" + HA2 + "!");
    String cnonce = authHeader.getCNonce();
    String KD = HA1 + ":" + nonce;
    if (cnonce != null) {
      KD += ":" + cnonce;
    }
    KD += ":" + HA2;
    mdbytes = messageDigest.digest(KD.getBytes());
    String mdString = ProxyUtilities.toHexString(mdbytes);
    String response = authHeader.getResponse();
    ProxyDebug.println(
        "DEBUG, DigestAuthenticateMethod, doAuthenticate(): "
            + "we have to compare his response: "
            + response
            + " with our computed"
            + " response: "
            + mdString);

    int res = (mdString.compareTo(response));
    if (res == 0) {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): " + "User authenticated...");
    } else {
      ProxyDebug.println(
          "DEBUG, DigestAuthenticateMethod, doAuthenticate(): " + "User not authenticated...");
    }

    return res == 0;
  }