System.Net.Security.NegotiateStream.BeginAuthenticateAsServer C# (CSharp) Method

        public virtual IAsyncResult BeginAuthenticateAsServer(AsyncCallback asyncCallback, object asyncState)
        {
            return BeginAuthenticateAsServer((NetworkCredential)CredentialCache.DefaultCredentials, null, ProtectionLevel.EncryptAndSign, TokenImpersonationLevel.Identification, asyncCallback, asyncState);
        }

 private void AcceptCallback(IAsyncResult ar)
 {
     try
     {
         Socket acceptSocket;
         acceptSocket = server.EndAccept(ar);
         nws = new NetworkStream(acceptSocket);
         ns = new NegotiateStream(nws);
         ns.BeginAuthenticateAsServer(AuthCallback, ns);
     }
     catch (Exception e)
     {
         Console.WriteLine(e.Message);
     }
 }