public Task Authenticated(SinaWeiBoAuthenticatedContext context)
 {
     return(OnAuthenticated(context));
 }
        protected override async Task <AuthenticationTicket> AuthenticateCoreAsync()
        {
            _logger.WriteVerbose("AuthenticateCore");

            AuthenticationProperties properties = null;

            try
            {
                string code  = null;
                string state = null;

                IReadableStringCollection query  = Request.Query;
                IList <string>            values = query.GetValues("code");
                if (values != null && values.Count == 1)
                {
                    code = values[0];
                }
                values = query.GetValues("state");
                if (values != null && values.Count == 1)
                {
                    state = values[0];
                }

                properties = Options.StateDataFormat.Unprotect(state);
                if (properties == null)
                {
                    return(null);
                }

                // OAuth2 10.12 CSRF
                if (!ValidateCorrelationId(properties, _logger))
                {
                    return(new AuthenticationTicket(null, properties));
                }

                var tokenRequestParameters = new List <KeyValuePair <string, string> >()
                {
                    new KeyValuePair <string, string>("client_id", Options.AppId),
                    new KeyValuePair <string, string>("client_secret", Options.AppSecret),
                    new KeyValuePair <string, string>("redirect_uri", GenerateRedirectUri()),
                    new KeyValuePair <string, string>("code", code),
                    new KeyValuePair <string, string>("grant_type", "authorization_code"),
                };

                FormUrlEncodedContent requestContent = new FormUrlEncodedContent(tokenRequestParameters);

                HttpResponseMessage response = await _httpClient.PostAsync(TokenEndpoint, requestContent, Request.CallCancelled);

                response.EnsureSuccessStatusCode();
                string oauthTokenResponse = await response.Content.ReadAsStringAsync();

                JObject oauth2Token = JObject.Parse(oauthTokenResponse);
                string  accessToken = oauth2Token["access_token"].Value <string>();

                if (string.IsNullOrWhiteSpace(accessToken))
                {
                    _logger.WriteWarning("Access token was not found");
                    return(new AuthenticationTicket(null, properties));
                }

                HttpResponseMessage userInfoResponse = await _httpClient.GetAsync(
                    UserInfoEndpoint + "?access_token=" + Uri.EscapeDataString(accessToken) + "&uid=" + oauth2Token["uid"].Value <string>(),
                    Request.CallCancelled);

                userInfoResponse.EnsureSuccessStatusCode();
                string accountString = await userInfoResponse.Content.ReadAsStringAsync();

                JObject accountInfo = JObject.Parse(accountString);

                string email = String.Empty;
                if (Options.RequireEmail)
                {
                    HttpResponseMessage emailResponse = await _httpClient.GetAsync(
                        EmailDetailEndpoint + "?access_token=" + Uri.EscapeDataString(accessToken),
                        Request.CallCancelled);

                    emailResponse.EnsureSuccessStatusCode();
                    string emailString = await emailResponse.Content.ReadAsStringAsync();

                    email = JObject.Parse(accountString)["email"].Value <string>();
                }

                var context = new SinaWeiBoAuthenticatedContext(Context, accountInfo, email, accessToken);
                context.Identity = new ClaimsIdentity(new[] {
                    new Claim(ClaimTypes.NameIdentifier, context.Id, XmlSchemaString, Options.AuthenticationType),
                    new Claim(ClaimsIdentity.DefaultNameClaimType, context.Name, XmlSchemaString, Options.AuthenticationType),
                    new Claim("urn:sinaweibo:id", context.Id, XmlSchemaString, Options.AuthenticationType),
                    new Claim("urn:sinaweibo:name", context.Name, XmlSchemaString, Options.AuthenticationType),
                });
                if (!String.IsNullOrWhiteSpace(context.Email))
                {
                    context.Identity.AddClaim(new Claim(ClaimTypes.Email, context.Email, XmlSchemaString, Options.AuthenticationType));
                }

                await Options.Provider.Authenticated(context);

                context.Properties = properties;

                return(new AuthenticationTicket(context.Identity, context.Properties));
            }
            catch (Exception ex)
            {
                _logger.WriteError(ex.Message);
            }

            return(new AuthenticationTicket(null, properties));
        }