private async Task <bool> InvokeReplyPathAsync()
        {
            if (Options.CallbackPath.HasValue && Options.CallbackPath == Request.Path)
            {
                // TODO: error responses

                AuthenticationTicket ticket = await AuthenticateAsync();

                if (ticket == null)
                {
                    logger.WriteWarning("Invalid return state, unable to redirect.");
                    Response.StatusCode = 500;
                    return(true);
                }

                var context = new TencentReturnEndpointContext(Context, ticket);
                context.SignInAsAuthenticationType = Options.SignInAsAuthenticationType;
                context.RedirectUri = ticket.Properties.RedirectUri;

                await Options.Provider.ReturnEndpoint(context);

                if (context.SignInAsAuthenticationType != null &&
                    context.Identity != null)
                {
                    ClaimsIdentity grantIdentity = context.Identity;
                    if (!string.Equals(grantIdentity.AuthenticationType, context.SignInAsAuthenticationType, StringComparison.Ordinal))
                    {
                        grantIdentity = new ClaimsIdentity(grantIdentity.Claims, context.SignInAsAuthenticationType, grantIdentity.NameClaimType, grantIdentity.RoleClaimType);
                    }
                    Context.Authentication.SignIn(context.Properties, grantIdentity);
                }

                if (!context.IsRequestCompleted && context.RedirectUri != null)
                {
                    string redirectUri = context.RedirectUri;
                    if (context.Identity == null)
                    {
                        // add a redirect hint that sign-in failed in some way
                        redirectUri = WebUtilities.AddQueryString(redirectUri, "error", "access_denied");
                    }
                    Response.Redirect(redirectUri);
                    context.RequestCompleted();
                }

                return(context.IsRequestCompleted);
            }
            return(false);
        }
        public async Task <bool> InvokeReturnPathAsync()
        {
            var ticket = await AuthenticateCoreAsync();

            if (ticket == null)
            {
                logger.WriteWarning("Invalid return state, unable to redirect.");
                Response.StatusCode = 500;
                return(true);
            }

            var context = new TencentReturnEndpointContext(Context, ticket)
            {
                SignInAsAuthenticationType = Options.SignInAsAuthenticationType,
                RedirectUri = ticket.Properties.RedirectUri
            };

            ticket.Properties.RedirectUri = null;

            await Options.Provider.ReturnEndpoint(context);

            if (context.Identity != null && context.SignInAsAuthenticationType != null)
            {
                var signInIdentity = context.Identity;
                if (!string.Equals(signInIdentity.AuthenticationType, context.SignInAsAuthenticationType, StringComparison.Ordinal))
                {
                    signInIdentity = new ClaimsIdentity(signInIdentity.Claims, context.SignInAsAuthenticationType, signInIdentity.NameClaimType, signInIdentity.RoleClaimType);
                }
                Context.Authentication.SignIn(context.Properties, signInIdentity);
            }
            if (!context.IsRequestCompleted && context.RedirectUri != null)
            {
                if (context.Identity == null)
                {
                    // add a redirect hint that sign-in failed in some way
                    context.RedirectUri = WebUtilities.AddQueryString(context.RedirectUri, "error", "access_denied");
                }
                Response.Redirect(context.RedirectUri);
                context.RequestCompleted();
            }

            return(context.IsRequestCompleted);
        }