NegotiateStream.RemoteIdentity Property

    public static void EndAuthenticateCallback (IAsyncResult ar)
    {
        // Get the saved data.
        ClientState cState = (ClientState) ar.AsyncState;
        TcpClient clientRequest = cState.Client;
        NegotiateStream authStream = (NegotiateStream) cState.AuthenticatedStream;
        Console.WriteLine("Ending authentication.");
        // Any exceptions that occurred during authentication are 
        // thrown by the EndAuthenticateAsServer method. 
        try 
        {
            // This call blocks until the authentication is complete.
            authStream.EndAuthenticateAsServer(ar);
        }
        catch (AuthenticationException e)
        {
            Console.WriteLine(e);
            Console.WriteLine("Authentication failed - closing connection.");
            cState.Waiter.Set();
            return;
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            Console.WriteLine("Closing connection.");
            cState.Waiter.Set();
            return;
        }
        // Display properties of the authenticated client.
        IIdentity id = authStream.RemoteIdentity;
        Console.WriteLine("{0} was authenticated using {1}.", 
            id.Name, 
            id.AuthenticationType
            );
        cState.Waiter.Set();

}