System.Net.Mail.SmtpNtlmAuthenticationModule.Authenticate C# (CSharp) Method

        public Authorization Authenticate(string challenge, NetworkCredential credential, object sessionCookie, string spn, ChannelBinding channelBindingToken)
        {
            if (NetEventSource.IsEnabled) NetEventSource.Enter(this, "Authenticate");
            try
            {
                lock (_sessions)
                {
                    NTAuthentication clientContext;
                    if (!_sessions.TryGetValue(sessionCookie, out clientContext))
                    {
                        if (credential == null)
                        {
                            return null;
                        }

                        _sessions[sessionCookie] =
                            clientContext =
                            new NTAuthentication(false, "Ntlm", credential, spn, ContextFlagsPal.Connection, channelBindingToken);

                    }

                    string resp = clientContext.GetOutgoingBlob(challenge);

                    if (!clientContext.IsCompleted)
                    {
                        return new Authorization(resp, false);
                    }
                    else
                    {
                        _sessions.Remove(sessionCookie);
                        return new Authorization(resp, true);
                    }
                }
            }
            // From reflected type NTAuthentication in System.Net.Security.
            catch (NullReferenceException)
            {
                return null;
            }
            finally
            {
                if (NetEventSource.IsEnabled) NetEventSource.Exit(this, "Authenticate");
            }
        }