Multithreaded server socket authentication

Go morning/afternoon/evening/good night

I am trying to find a way to make sure that every NEW connection needs to go through an authentication process before the server can accept connections from the client. However this should authentication procedure should not affect the clients who are already connected (the server should still continue receiving data from the already authenticated clients). The code I've got is:

import java.net.*;
import java.io.*;
import java.util.*;

/*
 * Class is used to authenticate the user
 */

public class PSWD implements Cloneable, Runnable
{
      Thread runner = null;
      ServerSocket pswd = null;
      Socket client = null;
      BufferedReader br = null;
      PrintWriter pw = null;
      boolean stop = false;
      static boolean authenticated = false;
      
      public synchronized void startPSWD(int port) throws IOException
      {
            if (runner == null)
            {
                  pswd = new ServerSocket(port);
                  runner = new Thread(this);
                  runner.start();
            }
      }

      public synchronized void stopPSWD()
      {
            if (pswd != null)
            {
                  stop = true;
                  runner.interrupt();
                  runner = null;
                  try
                  {
                        pswd.close();
                  }
                  catch (IOException ioe)
                  {
                        System.out.println("PSWD: Error");
                  }
                  pswd = null;
            }
      }

      public void run()
      {
            if (pswd != null)
            {
                  while (!stop)
                  {
                        try
                        {
                              Socket clientSocket = pswd.accept();
                              PSWD newPSWD = (PSWD) clone();

                              newPSWD.pswd = null;
                              newPSWD.client = clientSocket;
                              newPSWD.runner = new Thread(newPSWD);
                              newPSWD.runner.start();
                        }
                        catch (Exception e)
                        {
                        }
                  }
            }
            else
            {
                  run(client);
            }
      }

      public void run(Socket client)
      {
            try
          {
                br = new BufferedReader(new InputStreamReader(client.getInputStream()));
                pw = new PrintWriter(client.getOutputStream(), true);
          }
          catch (IOException ioe)
          {
                  System.out.println("PSWD: Streams failed");
                  System.exit(-1);
          }
}

I'm not too worried about the authentication class at this stage, my primary concern is that if I set an arbitrary boolean value to false I wouldn't affect the clients already connected.

Pseudo code / stubs would be good but example code would be even better.