AcquireTokenByAuthorizationCodeAsync does not complete - asp.net-mvc

Question

Here is my code. It's been over a month I'm trying to add calendars in Outlook but nothing is working :( please help. The function AcquireTokenByAuthorizationCodeAsync never completes. And the token.Result is always null
string authority = ConfigurationManager.AppSettings["authority"];
string clientID = ConfigurationManager.AppSettings["clientID"];
Uri clientAppUri = new Uri(ConfigurationManager.AppSettings["clientAppUri"]);
string serverName = ConfigurationManager.AppSettings["serverName"];
var code = Request.Params["code"];
AuthenticationContext ac = new AuthenticationContext(authority, true);
ClientCredential clcred = new ClientCredential(clientid, secretkey);
//ac = ac.AcquireToken(serverName, clientID, clientAppUri, PromptBehavior.Auto);
//string to = ac.AcquireToken(serverName, clientID, clientAppUri, PromptBehavior.Auto).AccessToken;
var token = ac.AcquireTokenByAuthorizationCodeAsync(code, new Uri("http://localhost:2694/GetAuthCode/Index/"), clcred, resource: "https://graph.microsoft.com/");
string newtoken = token.Result.AccessToken;
ExchangeService exchangeService = new ExchangeService(ExchangeVersion.Exchange2013);
exchangeService.Url = new Uri("https://outlook.office365.com/" + "ews/exchange.asmx");
exchangeService.TraceEnabled = true;
exchangeService.TraceFlags = TraceFlags.All;
exchangeService.Credentials = new OAuthCredentials(token.Result.AccessToken);
exchangeService.FindFolders(WellKnownFolderName.Root, new FolderView(10));
Appointment app = new Appointment(exchangeService);
app.Subject = "";
app.Body = "";
app.Location = "";
app.Start = DateTime.Now;
app.End = DateTime.Now.AddDays(1);
app.Save(SendInvitationsMode.SendToAllAndSaveCopy);

Answer 1

I have experienced this issue when I call the AcquireTokenByAuthorizationCodeAsync using result instead of using await key words and all these code was in a asynchronously controller in the MVC.
If you are in the same scenario, you can fix this issue by two ways:
1.Always using the async, await like code below:
public async System.Threading.Tasks.Task<ActionResult> About()
{
...
var result =await ac.AcquireTokenByAuthorizationCodeAsync(code, new Uri("http://localhost:2694/GetAuthCode/Index/"), clcred, resource: "https://graph.microsoft.com/");
var accessToken = result.AccessToken;
...
}
2.Use the synchronization controller:
public void About()
{
...
var result =ac.AcquireTokenByAuthorizationCodeAsync(code, new Uri("http://localhost:2694/GetAuthCode/Index/"), clcred, resource: "https://graph.microsoft.com/").Result;
var accessToken = result.AccessToken;
...
}