Adding 2FA Authenticator Support (#66)

* Adding support for 2fa, more auth options

* WIP getting auth stuff working

* Added Manage views. 2FA working now for MVC app.

* Switching to using a controller for no-UI logout scenario

* Adding Razor Pages impl of 2FA auth stuff. Works.

src/Web/Views/Manage/ManageNavPages.cs

@@ -0,0 +1,35 @@
+using System;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+
+namespace Microsoft.eShopWeb.Views.Manage
+{
+    public static class ManageNavPages
+    {
+        public static string ActivePageKey => "ActivePage";
+
+        public static string Index => "Index";
+
+        public static string ChangePassword => "ChangePassword";
+
+        public static string ExternalLogins => "ExternalLogins";
+
+        public static string TwoFactorAuthentication => "TwoFactorAuthentication";
+
+        public static string IndexNavClass(ViewContext viewContext) => PageNavClass(viewContext, Index);
+
+        public static string ChangePasswordNavClass(ViewContext viewContext) => PageNavClass(viewContext, ChangePassword);
+
+        public static string ExternalLoginsNavClass(ViewContext viewContext) => PageNavClass(viewContext, ExternalLogins);
+
+        public static string TwoFactorAuthenticationNavClass(ViewContext viewContext) => PageNavClass(viewContext, TwoFactorAuthentication);
+    
+        public static string PageNavClass(ViewContext viewContext, string page)
+        {
+            var activePage = viewContext.ViewData["ActivePage"] as string;
+            return string.Equals(activePage, page, StringComparison.OrdinalIgnoreCase) ? "active" : null;
+        }
+
+        public static void AddActivePage(this ViewDataDictionary viewData, string activePage) => viewData[ActivePageKey] = activePage;
+    }
+}