o365 calendar API not returning calendar - calendar

Question

I am following instructions provided at https://dev.outlook.com/RestGettingStarted/Tutorial/dotnet to get my web application integrated with user's outlook calendar. I am being redirected to login into my microsoft account and it returns to my return url with the code parameter populated. However when I try to generate token out of that code it returns empty without any error.
Can someone please advise?
Following code is to generate token from the code:
// Note the function signature is changed!
public async Task<ActionResult> Authorize()
{
// Get the 'code' parameter from the Azure redirect
string authCode = Request.Params["code"];
string authority = "https://login.microsoftonline.com/common";
string clientId = System.Configuration.ConfigurationManager.AppSettings["ida:ClientID"];
string clientSecret = System.Configuration.ConfigurationManager.AppSettings["ida:ClientSecret"];
AuthenticationContext authContext = new AuthenticationContext(authority);
// The same url we specified in the auth code request
Uri redirectUri = new Uri(Url.Action("Authorize", "Home", null, Request.Url.Scheme));
// Use client ID and secret to establish app identity
ClientCredential credential = new ClientCredential(clientId, clientSecret);
try
{
// Get the token
var authResult = await authContext.AcquireTokenByAuthorizationCodeAsync(
authCode, redirectUri, credential, scopes);
// Save the token in the session
Session["access_token"] = authResult.Token;
// Try to get user info
Session["user_email"] = GetUserEmail(authContext, clientId);
return Content("Access Token: " + authResult.Token);
}
catch (AdalException ex)
{
return Content(string.Format("ERROR retrieving token: {0}", ex.Message));
}
}