Update 07082021

WebFormApp/Account/OpenAuthProviders.ascx.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Web;
+using Microsoft.AspNet.Identity;
+using Microsoft.Owin.Security;
+
+namespace WebFormApp.Account
+{
+    public partial class OpenAuthProviders : System.Web.UI.UserControl
+    {
+        protected void Page_Load(object sender, EventArgs e)
+        {
+            if (IsPostBack)
+            {
+                var provider = Request.Form["provider"];
+                if (provider == null)
+                {
+                    return;
+                }
+                // Umleitung an den externen Anmeldeanbieter anfordern
+                string redirectUrl = ResolveUrl(String.Format(CultureInfo.InvariantCulture, "~/Account/RegisterExternalLogin?{0}={1}&returnUrl={2}", IdentityHelper.ProviderNameKey, provider, ReturnUrl));
+                var properties = new AuthenticationProperties() { RedirectUri = redirectUrl };
+                // XSRF-Überprüfung beim Verknüpfen von Konten hinzufügen
+                if (Context.User.Identity.IsAuthenticated)
+                {
+                    properties.Dictionary[IdentityHelper.XsrfKey] = Context.User.Identity.GetUserId();
+                }
+                Context.GetOwinContext().Authentication.Challenge(properties, provider);
+                Response.StatusCode = 401;
+                Response.End();
+            }
+        }
+
+        public string ReturnUrl { get; set; }
+
+        public IEnumerable<string> GetProviderNames()
+        {
+            return Context.GetOwinContext().Authentication.GetExternalAuthenticationTypes().Select(t => t.AuthenticationType);
+        }
+    }
+}