MVC ACS Redirection (OWA and Rich Client)

gistfile1.cs

using System;
using System.Configuration;
using System.Threading.Tasks;
using System.Web.Mvc;
using Microsoft.IdentityModel.Clients.ActiveDirectory;

namespace Demo_DemoFinal_MVC5.Controllers
{
    public class HomeController : Controller
    {
        private readonly string _clientId = ConfigurationManager.AppSettings["ida:ClientID"];
        private readonly string _appKey = ConfigurationManager.AppSettings["ida:Password"];
        private readonly string _authorizationUri = ConfigurationManager.AppSettings["ida:AuthorizationUri"];

        private const string ServiceResourceId = "https://<tenant>.sharepoint.com";

        public async Task<ActionResult> Index(string et, string code, string error, string error_description)
        {
            if (error != null) return RedirectToAction("Error", new {error, error_description});

            var authContext = new AuthenticationContext(_authorizationUri + "/common", true);

            // Check if you received an authorization code, if not you need to sign in
            if (code == null)
            {
                // Get the authorization URL (https://login.windows.net/common/oauth2/authorize)
                var redirectUri = authContext.GetAuthorizationRequestURL(ServiceResourceId, _clientId, new Uri(Request.Url.AbsoluteUri.Split('?')[0]), UserIdentifier.AnyUser, string.Empty);

                // Redirect the client based on the context (Rich Client or Online)
                if (et == null)
                {
                    return Redirect(redirectUri.ToString());
                }
                @ViewBag.URL = redirectUri.ToString();
                return View();
            }

            // If the code is empty, show the user the error page
            if (String.IsNullOrEmpty(code)) return RedirectToAction("Error", new { error = "AuthToken", error_description = "The authorization token was not retrieved."});

            // If a code is retrieved, the access token can be generated
            var clientCredentials = new ClientCredential(_clientId, _appKey);
            var authResult = await authContext.AcquireTokenByAuthorizationCodeAsync(code, new Uri(Request.Url.AbsoluteUri.Split('?')[0]), clientCredentials);
            Session["AccessToken"] = authResult.AccessToken;

            return RedirectToAction("SiteInfo");
        }

        public ActionResult SiteInfo()
        {
            var accessToken = Session["AccessToken"].ToString();
            if (!string.IsNullOrEmpty(accessToken))
            {
                using(var clientContext = TokenHelper.GetClientContextWithAccessToken(ServiceResourceId, accessToken)) {
                    var web = clientContext.Web;
                    clientContext.Load(web, w => w.Title, w => w.CurrentUser.Title);
                    clientContext.ExecuteQuery();
    
                    ViewBag.SiteTitle = web.Title;
                    ViewBag.User = web.CurrentUser.Title;
                }
            }
            return View();
        }

        public ActionResult Error(string error, string error_description)
        {
            ViewBag.Error = error;
            ViewBag.Desc = error_description;
            return View();
        }
    }
}