public boolean authenticate(
      String[] mechs, final String realm, final String authzid, final String u, final String p)
      throws ProtocolException {

    synchronized (pr) { // authenticate method should be synchronized
      List<Response> v = new ArrayList<Response>();
      String tag = null;
      Response r = null;
      boolean done = false;
      if (logger.isLoggable(Level.FINE)) {
        logger.fine("SASL Mechanisms:");
        for (int i = 0; i < mechs.length; i++) logger.fine(" " + mechs[i]);
        logger.fine("");
      }

      SaslClient sc;
      CallbackHandler cbh =
          new CallbackHandler() {
            public void handle(Callback[] callbacks) {
              if (logger.isLoggable(Level.FINE))
                logger.fine("SASL callback length: " + callbacks.length);
              for (int i = 0; i < callbacks.length; i++) {
                if (logger.isLoggable(Level.FINE))
                  logger.fine("SASL callback " + i + ": " + callbacks[i]);
                if (callbacks[i] instanceof NameCallback) {
                  NameCallback ncb = (NameCallback) callbacks[i];
                  ncb.setName(u);
                } else if (callbacks[i] instanceof PasswordCallback) {
                  PasswordCallback pcb = (PasswordCallback) callbacks[i];
                  pcb.setPassword(p.toCharArray());
                } else if (callbacks[i] instanceof RealmCallback) {
                  RealmCallback rcb = (RealmCallback) callbacks[i];
                  rcb.setText(realm != null ? realm : rcb.getDefaultText());
                } else if (callbacks[i] instanceof RealmChoiceCallback) {
                  RealmChoiceCallback rcb = (RealmChoiceCallback) callbacks[i];
                  if (realm == null) rcb.setSelectedIndex(rcb.getDefaultChoice());
                  else {
                    // need to find specified realm in list
                    String[] choices = rcb.getChoices();
                    for (int k = 0; k < choices.length; k++) {
                      if (choices[k].equals(realm)) {
                        rcb.setSelectedIndex(k);
                        break;
                      }
                    }
                  }
                }
              }
            }
          };

      try {
        sc = Sasl.createSaslClient(mechs, authzid, name, host, (Map) props, cbh);
      } catch (SaslException sex) {
        logger.log(Level.FINE, "Failed to create SASL client", sex);
        throw new UnsupportedOperationException(sex.getMessage(), sex);
      }
      if (sc == null) {
        logger.fine("No SASL support");
        throw new UnsupportedOperationException("No SASL support");
      }
      if (logger.isLoggable(Level.FINE)) logger.fine("SASL client " + sc.getMechanismName());

      try {
        Argument args = new Argument();
        args.writeAtom(sc.getMechanismName());
        if (pr.hasCapability("SASL-IR") && sc.hasInitialResponse()) {
          String irs;
          byte[] ba = sc.evaluateChallenge(new byte[0]);
          if (ba.length > 0) {
            ba = BASE64EncoderStream.encode(ba);
            irs = ASCIIUtility.toString(ba, 0, ba.length);
          } else irs = "=";
          args.writeAtom(irs);
        }
        tag = pr.writeCommand("AUTHENTICATE", args);
      } catch (Exception ex) {
        logger.log(Level.FINE, "SASL AUTHENTICATE Exception", ex);
        return false;
      }

      OutputStream os = pr.getIMAPOutputStream(); // stream to IMAP server

      /*
       * Wrap a BASE64Encoder around a ByteArrayOutputstream
       * to craft b64 encoded username and password strings
       *
       * Note that the encoded bytes should be sent "as-is" to the
       * server, *not* as literals or quoted-strings.
       *
       * Also note that unlike the B64 definition in MIME, CRLFs
       * should *not* be inserted during the encoding process. So, I
       * use Integer.MAX_VALUE (0x7fffffff (> 1G)) as the bytesPerLine,
       * which should be sufficiently large !
       */

      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      byte[] CRLF = {(byte) '\r', (byte) '\n'};

      // Hack for Novell GroupWise XGWTRUSTEDAPP authentication mechanism
      // http://www.novell.com/developer/documentation/gwimap/?
      //   page=/developer/documentation/gwimap/gwimpenu/data/al7te9j.html
      boolean isXGWTRUSTEDAPP =
          sc.getMechanismName().equals("XGWTRUSTEDAPP")
              && PropUtil.getBooleanProperty(
                  props, "mail." + name + ".sasl.xgwtrustedapphack.enable", true);
      while (!done) { // loop till we are done
        try {
          r = pr.readResponse();
          if (r.isContinuation()) {
            byte[] ba = null;
            if (!sc.isComplete()) {
              ba = r.readByteArray().getNewBytes();
              if (ba.length > 0) ba = BASE64DecoderStream.decode(ba);
              if (logger.isLoggable(Level.FINE))
                logger.fine("SASL challenge: " + ASCIIUtility.toString(ba, 0, ba.length) + " :");
              ba = sc.evaluateChallenge(ba);
            }
            if (ba == null) {
              logger.fine("SASL no response");
              os.write(CRLF); // write out empty line
              os.flush(); // flush the stream
              bos.reset(); // reset buffer
            } else {
              if (logger.isLoggable(Level.FINE))
                logger.fine("SASL response: " + ASCIIUtility.toString(ba, 0, ba.length) + " :");
              ba = BASE64EncoderStream.encode(ba);
              if (isXGWTRUSTEDAPP) bos.write(ASCIIUtility.getBytes("XGWTRUSTEDAPP "));
              bos.write(ba);

              bos.write(CRLF); // CRLF termination
              os.write(bos.toByteArray()); // write out line
              os.flush(); // flush the stream
              bos.reset(); // reset buffer
            }
          } else if (r.isTagged() && r.getTag().equals(tag))
            // Ah, our tagged response
            done = true;
          else if (r.isBYE()) // outta here
          done = true;
          else // hmm .. unsolicited response here ?!
          v.add(r);
        } catch (Exception ioex) {
          logger.log(Level.FINE, "SASL Exception", ioex);
          // convert this into a BYE response
          r = Response.byeResponse(ioex);
          done = true;
          // XXX - ultimately return true???
        }
      }

      if (sc.isComplete() /*&& res.status == SUCCESS*/) {
        String qop = (String) sc.getNegotiatedProperty(Sasl.QOP);
        if (qop != null
            && (qop.equalsIgnoreCase("auth-int") || qop.equalsIgnoreCase("auth-conf"))) {
          // XXX - NOT SUPPORTED!!!
          logger.fine("SASL Mechanism requires integrity or confidentiality");
          return false;
        }
      }

      /* Dispatch untagged responses.
       * NOTE: in our current upper level IMAP classes, we add the
       * responseHandler to the Protocol object only *after* the
       * connection has been authenticated. So, for now, the below
       * code really ends up being just a no-op.
       */
      Response[] responses = v.toArray(new Response[v.size()]);
      pr.notifyResponseHandlers(responses);

      // Handle the final OK, NO, BAD or BYE response
      pr.handleResult(r);
      pr.setCapabilities(r);

      /*
       * If we're using the Novell Groupwise XGWTRUSTEDAPP mechanism
       * to run as a specified authorization ID, we have to issue a
       * LOGIN command to select the user we want to operate as.
       */
      if (isXGWTRUSTEDAPP && authzid != null) {
        Argument args = new Argument();
        args.writeString(authzid);

        responses = pr.command("LOGIN", args);

        // dispatch untagged responses
        pr.notifyResponseHandlers(responses);

        // Handle result of this command
        pr.handleResult(responses[responses.length - 1]);
        // If the response includes a CAPABILITY response code, process it
        pr.setCapabilities(responses[responses.length - 1]);
      }
      return true;
    }
  }
  public static void main(String[] args) throws Exception {
    if (args.length == 0) {
      namesfile = null;
      auto = true;
    } else {
      int i = 0;
      if (args[i].equals("-m")) {
        i++;
        auto = false;
      }
      if (args.length > i) {
        namesfile = args[i++];
        if (args.length > i) {
          proxyfile = args[i];
        }
      } else {
        namesfile = null;
      }
    }

    CallbackHandler clntCbh = null;
    final CallbackHandler srvCbh = new PropertiesFileCallbackHandler(null, namesfile, proxyfile);

    Subject clntSubj = doLogin("client");
    Subject srvSubj = doLogin("server");
    final HashMap clntprops = new HashMap();
    final HashMap srvprops = new HashMap();

    clntprops.put(Sasl.QOP, "auth");
    srvprops.put(Sasl.QOP, "auth,auth-int,auth-conf");

    final SaslClient clnt =
        (SaslClient)
            Subject.doAs(
                clntSubj,
                new PrivilegedExceptionAction() {
                  public Object run() throws Exception {
                    return Sasl.createSaslClient(
                        new String[] {MECH}, null, PROTOCOL, SERVER_FQDN, clntprops, null);
                  }
                });

    if (verbose) {
      System.out.println(clntSubj);
      System.out.println(srvSubj);
    }
    final SaslServer srv =
        (SaslServer)
            Subject.doAs(
                srvSubj,
                new PrivilegedExceptionAction() {
                  public Object run() throws Exception {
                    return Sasl.createSaslServer(MECH, PROTOCOL, SERVER_FQDN, srvprops, srvCbh);
                  }
                });

    if (clnt == null) {
      throw new IllegalStateException("Unable to find client impl for " + MECH);
    }
    if (srv == null) {
      throw new IllegalStateException("Unable to find server impl for " + MECH);
    }

    byte[] response;
    byte[] challenge;

    response =
        (byte[])
            Subject.doAs(
                clntSubj,
                new PrivilegedExceptionAction() {
                  public Object run() throws Exception {
                    return (clnt.hasInitialResponse() ? clnt.evaluateChallenge(EMPTY) : EMPTY);
                  }
                });

    while (!clnt.isComplete() || !srv.isComplete()) {
      final byte[] responseCopy = response;
      challenge =
          (byte[])
              Subject.doAs(
                  srvSubj,
                  new PrivilegedExceptionAction() {
                    public Object run() throws Exception {
                      return srv.evaluateResponse(responseCopy);
                    }
                  });

      if (challenge != null) {
        final byte[] challengeCopy = challenge;
        response =
            (byte[])
                Subject.doAs(
                    clntSubj,
                    new PrivilegedExceptionAction() {
                      public Object run() throws Exception {
                        return clnt.evaluateChallenge(challengeCopy);
                      }
                    });
      }
    }

    if (clnt.isComplete() && srv.isComplete()) {
      if (verbose) {
        System.out.println("SUCCESS");
        System.out.println("authzid is " + srv.getAuthorizationID());
      }
    } else {
      throw new IllegalStateException(
          "FAILURE: mismatched state:"
              + " client complete? "
              + clnt.isComplete()
              + " server complete? "
              + srv.isComplete());
    }

    if (verbose) {
      System.out.println(clnt.getNegotiatedProperty(Sasl.QOP));
    }

    // Now try to use security layer

    byte[] clntBuf = new byte[] {0, 1, 2, 3};
    try {
      byte[] wrapped = clnt.wrap(clntBuf, 0, clntBuf.length);
      throw new Exception("clnt wrap should not be allowed w/no security layer");
    } catch (IllegalStateException e) {
      // expected
    }

    byte[] srvBuf = new byte[] {10, 11, 12, 13};
    try {
      byte[] wrapped = srv.wrap(srvBuf, 0, srvBuf.length);
      throw new Exception("srv wrap should not be allowed w/no security layer");
    } catch (IllegalStateException e) {
      // expected
    }

    try {
      byte[] unwrapped = clnt.unwrap(clntBuf, 0, clntBuf.length);
      throw new Exception("clnt wrap should not be allowed w/no security layer");
    } catch (IllegalStateException e) {
      // expected
    }

    try {
      byte[] unwrapped = srv.unwrap(srvBuf, 0, srvBuf.length);
      throw new Exception("srv wrap should not be allowed w/no security layer");
    } catch (IllegalStateException e) {
      // expected
    }
  }