[Wait for GA] Update SystemWebAdapters API from obsolete AddSystemWebAdapters to HttpApplicationHost.RegisterHost (#36198)

* Initial plan

* Update obsolete SystemWebAdapters API to HttpApplicationHost.RegisterHost

Co-authored-by: wadepickett <10985336+wadepickett@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wadepickett <10985336+wadepickett@users.noreply.github.com>

Author: Copilot

aspnetcore/migration/fx-to-core/areas/authentication/samples/AspNetApp.cs

@@ -14,13 +14,16 @@ protected void Application_Start()
         BundleConfig.RegisterBundles(BundleTable.Bundles);
 
         // <snippet_SystemWebAdapterConfiguration>
-        SystemWebAdapterConfiguration.AddSystemWebAdapters(this)
-            .AddProxySupport(options => options.UseForwardedHeaders = true)
-            .AddRemoteAppServer(options =>
-            {
-                options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"];
-            })
-            .AddAuthenticationServer();
+        HttpApplicationHost.RegisterHost(builder =>
+        {
+            builder.AddSystemWebAdapters()
+                .AddProxySupport(options => options.UseForwardedHeaders = true)
+                .AddRemoteAppServer(options =>
+                {
+                    options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"];
+                })
+                .AddAuthenticationServer();
+        });
         // </snippet_SystemWebAdapterConfiguration>
     }
 }

aspnetcore/migration/fx-to-core/areas/session/samples/remote/Global.asax.cs

@@ -2,16 +2,19 @@ public class Global : HttpApplication
 {
         protected void Application_Start()
         {
-            SystemWebAdapterConfiguration.AddSystemWebAdapters(this)
-                .AddJsonSessionSerializer(options =>
-                {
-                    // Serialization/deserialization requires each session key to be registered to a type
-                    options.RegisterKey<int>("test-value");
-                    options.RegisterKey<SessionDemoModel>("SampleSessionItem");
-                })
-                // Provide a strong API key that will be used to authenticate the request on the remote app for querying the session
-                // ApiKey is a string representing a GUID
-                .AddRemoteAppServer(options => options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"])
-                .AddSessionServer();
+            HttpApplicationHost.RegisterHost(builder =>
+            {
+                builder.AddSystemWebAdapters()
+                    .AddJsonSessionSerializer(options =>
+                    {
+                        // Serialization/deserialization requires each session key to be registered to a type
+                        options.RegisterKey<int>("test-value");
+                        options.RegisterKey<SessionDemoModel>("SampleSessionItem");
+                    })
+                    // Provide a strong API key that will be used to authenticate the request on the remote app for querying the session
+                    // ApiKey is a string representing a GUID
+                    .AddRemoteAppServer(options => options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"])
+                    .AddSessionServer();
+            });
         }
 }

aspnetcore/migration/fx-to-core/inc/remote-app-setup.md

@@ -4,7 +4,7 @@ description: Remote app setup
 author: wadepickett
 ms.author: wpickett
 monikerRange: '>= aspnetcore-6.0'
-ms.date: 09/16/2025
+ms.date: 10/08/2025
 ms.topic: article
 uid: migration/fx-to-core/inc/remote-app-setup
 zone_pivot_groups: migration-remote-app-setup
@@ -61,12 +61,15 @@ To configure the application to be available to handle the requests from the ASP
     ```CSharp
     protected void Application_Start()
     {
-        SystemWebAdapterConfiguration.AddSystemWebAdapters(this)
-            .AddRemoteAppServer(options =>
-            {
-                // ApiKey is a string representing a GUID
-                options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"];
-            });
+        HttpApplicationHost.RegisterHost(builder =>
+        {
+            builder.AddSystemWebAdapters()
+                .AddRemoteAppServer(options =>
+                {
+                    // ApiKey is a string representing a GUID
+                    options.ApiKey = System.Configuration.ConfigurationManager.AppSettings["RemoteAppApiKey"];
+                });
+        });
 
         // ...existing code...
     }