public async Task Callback()

in OAuthWebSample/OAuthWebSample/Controllers/OAuthController.cs [65:109]
36 lines of code
4 McCabe index (conditional complexity)

        public async Task<ActionResult> Callback(String code, Guid state)
        {
            String error;
            if (ValidateCallbackValues(code, state.ToString(), out error))
            {
                // Exchange the auth code for an access token and refresh token
                HttpRequestMessage requestMessage = new HttpRequestMessage(HttpMethod.Post, ConfigurationManager.AppSettings["TokenUrl"]);
                requestMessage.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

                Dictionary<String, String> form = new Dictionary<String, String>()
                {
                    { "client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer" },
                    { "client_assertion", ConfigurationManager.AppSettings["ClientAppSecret"] },
                    { "grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer" },
                    { "assertion", code },
                    { "redirect_uri", ConfigurationManager.AppSettings["CallbackUrl"] }
                };
                requestMessage.Content = new FormUrlEncodedContent(form);

                HttpResponseMessage responseMessage = await s_httpClient.SendAsync(requestMessage);

                if (responseMessage.IsSuccessStatusCode)
                {
                    String body = await responseMessage.Content.ReadAsStringAsync();

                    TokenModel tokenModel = s_authorizationRequests[state];
                    JsonConvert.PopulateObject(body, tokenModel);
                    
                    ViewBag.Token = tokenModel;
                }
                else
                {
                    error = responseMessage.ReasonPhrase;
                }
            }

            if (!String.IsNullOrEmpty(error))
            {
                ViewBag.Error = error;
            }

            ViewBag.ProfileUrl = ConfigurationManager.AppSettings["ProfileUrl"];

            return View("TokenView");
        }