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/ViewModels/Manage/EnableAuthenticatorViewModel.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel;
+using System.ComponentModel.DataAnnotations;
+
+namespace Microsoft.eShopWeb.ViewModels.Manage
+{
+    public class EnableAuthenticatorViewModel
+    {
+        [Required]
+        [StringLength(7, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)]
+        [DataType(DataType.Text)]
+        [Display(Name = "Verification Code")]
+        public string Code { get; set; }
+
+        [ReadOnly(true)]
+        public string SharedKey { get; set; }
+
+        public string AuthenticatorUri { get; set; }
+    }
+}