This section details on the original issue you should resolve

<issue_title>SystemWebAdapterConfiguration.AddSystemWebAdapters(HttpApplication)' is obsolete: 'Prefer using HttpApplicationHost.RegisterHost(...) instead</issue_title>
<issue_description>### Description

Hi Wade

Step 2 in Configure ASP.NET Framework Application is out of date. It generates a

warning CS0618: 'SystemWebAdapterConfiguration.AddSystemWebAdapters(HttpApplication)' is obsolete: 'Prefer using HttpApplicationHost.RegisterHost(...) instead'

I believe the code should be something like this:

 HttpApplicationHost.RegisterHost(builder =>
 {
 builder.AddServiceDefaults();
 builder.RegisterWebObjectActivator();
 builder.AddSystemWebAdapters()
 .AddVirtualizedContentDirectories();
 builder.AddSystemWebAdapters()
 .AddRemoteAppServer(options =>
 {
 // ApiKey is a string representing a GUID
 options.ApiKey = System.Configuration.ConfigurationManager.AppSettings["RemoteAppApiKey"];
 });
 });

Also, we are having trouble trying to get the recipe to work. We have adapted the https://github.com/dotnet/systemweb-adapters/tree/main sample to work using a domain setup (have set up two domains as framework.noho.ca and core.noho.ca) on our dev machines. We can log in to framework and then when we try to load the core app, it does not pick up the login details even though it does have the shared cookie. There are no errors and we are a bit fuzzy regarding the communication mechanism between the two.

Do you know of any example code which show the domain version using the manual setup? We got the Aspire version to run from the sample using the local host and the dashboard and could see login in the core app, and are trying to get a version running that we could apply to our main app. It is a very large project with a million lines of combined code.

Page URL

https://learn.microsoft.com/en-us/aspnet/core/migration/fx-to-core/inc/remote-app-setup?view=aspnetcore-9.0&pivots=manual

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/migration/fx-to-core/inc/remote-app-setup.md

Document ID

f3b2ce81-5438-1d1a-1c2b-6cc9a089a0ea

Platform Id

f8610778-e458-a8a6-8136-0ee8c72f11e8

Article author

@wadepickett

Metadata

• ID: f3b2ce81-5438-1d1a-1c2b-6cc9a089a0ea
• PlatformId: f8610778-e458-a8a6-8136-0ee8c72f11e8
• Service: aspnet-core
• Sub-service: migration

Related Issues</issue_description>

Comments on the Issue (you are @copilot in this section)

Triage notes and draft action plan:

Issue Summary

This is a valid issue. The article "Remote app setup" instructs users to use SystemWebAdapterConfiguration.AddSystemWebAdapters(this) in Global.asax.cs for ASP.NET Framework configuration. As of the latest SystemWebAdapters packages, this API is obsolete and emits CS0618, advising use of HttpApplicationHost.RegisterHost(...) instead. The article does not reflect this change and needs to be updated to prevent confusion and ensure best practices.

Action Items

• Update aspnetcore/migration/fx-to-core/inc/remote-app-setup.md lines 59–73 and any other occurrences of the obsolete API.
• Add additional troubleshooting and real-world setup guidance as requested.
• Confirm sample code matches updated APIs.

Details for Action Plan

Files Impacted

• aspnetcore/migration/fx-to-core/inc/remote-app-setup.md
  • Section: Configure ASP.NET Framework Application
  • Lines: 59–73 (code block using obsolete API)
  • Potential impact: Other sections may also need to reference the new API if it is mentioned elsewhere.

Required Changes

1. Replace obsolete API usage

Current code (lines 62–73):

protected void Application_Start()
{
 SystemWebAdapterConfiguration.AddSystemWebAdapters(this)
 .AddRemoteAppServer(options =>
 {
 // ApiKey is a string representing a GUID
 options.ApiKey = ConfigurationManager.AppSettings["RemoteAppApiKey"];
 });
 // ...existing code...
}

Replace with:

protected void Application_Start()
{
 HttpApplicationHost.RegisterHost(builder =>
 {
 builder.AddServiceDefaults();
 builder.RegisterWebObjectActivator();
 builder.AddSystemWebAdapters()
 .AddVirtualizedContentDirectories();
 builder.AddS...
</details>
Fixes dotnet/AspNetCore.Docs#36197
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#### Internal previews
| 📄 File | 🔗 Preview link |
|:--|:--|
| [aspnetcore/migration/fx-to-core/inc/remote-app-setup.md](https://github.com/dotnet/AspNetCore.Docs/blob/0be75490ea40cf2f65e45dadd308fc8bfc6347f4/aspnetcore/migration/fx-to-core/inc/remote-app-setup.md) | [aspnetcore/migration/fx-to-core/inc/remote-app-setup](https://review.learn.microsoft.com/en-us/aspnet/core/migration/fx-to-core/inc/remote-app-setup?branch=pr-en-us-36198) |
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