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/EnableAuthenticator.cshtml

@@ -0,0 +1,52 @@
+@model EnableAuthenticatorViewModel
+@{
+    ViewData["Title"] = "Enable authenticator";
+    ViewData.AddActivePage(ManageNavPages.TwoFactorAuthentication);
+}
+
+<h4>@ViewData["Title"]</h4>
+<div>
+    <p>To use an authenticator app go through the following steps:</p>
+    <ol class="list">
+        <li>
+            <p>
+                Download a two-factor authenticator app like Microsoft Authenticator for
+                <a href="https://go.microsoft.com/fwlink/?Linkid=825071">Windows Phone</a>,
+                <a href="https://go.microsoft.com/fwlink/?Linkid=825072">Android</a> and
+                <a href="https://go.microsoft.com/fwlink/?Linkid=825073">iOS</a> or
+                Google Authenticator for
+                <a href="https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2&amp;hl=en">Android</a> and
+                <a href="https://itunes.apple.com/us/app/google-authenticator/id388497605?mt=8">iOS</a>.
+            </p>
+        </li>
+        <li>
+            <p>Scan the QR Code or enter this key <kbd>@Model.SharedKey</kbd> into your two factor authenticator app. Spaces and casing do not matter.</p>
+            <div class="alert alert-info">To enable QR code generation please read our <a href="https://go.microsoft.com/fwlink/?Linkid=852423">documentation</a>.</div>
+            <div id="qrCode"></div>
+            <div id="qrCodeData" data-url="@Html.Raw(Model.AuthenticatorUri)"></div>
+        </li>
+        <li>
+            <p>
+                Once you have scanned the QR code or input the key above, your two factor authentication app will provide you
+                with a unique code. Enter the code in the confirmation box below.
+            </p>
+            <div class="row">
+                <div class="col-md-6">
+                    <form method="post">
+                        <div class="form-group">
+                            <label asp-for="Code" class="control-label">Verification Code</label>
+                            <input asp-for="Code" class="form-control" autocomplete="off" />
+                            <span asp-validation-for="Code" class="text-danger"></span>
+                        </div>
+                        <button type="submit" class="btn btn-default">Verify</button>
+                        <div asp-validation-summary="ModelOnly" class="text-danger"></div>
+                    </form>
+                </div>
+            </div>
+        </li>
+    </ol>
+</div>
+
+@section Scripts {
+    @await Html.PartialAsync("_ValidationScriptsPartial")
+}