add request services

Author: twsouthwick

aspnetcore/migration/fx-to-core/areas/hosting.md

@@ -70,7 +70,7 @@ This extension method is an internal method that will be source generated depend
 
 - WebForms and handlers using the <xref:System.Web.HttpRuntime.WebObjectActivator>
 - ASP.NET MVC using <xref:System.Web.Mvc.DependencyResolver>
-- ASP.NET WebApi using [DependencyResolver](https://learn.microsoft.com/en-us/previous-versions/aspnet/hh969140(v=vs.108))
+- ASP.NET WebApi using [DependencyResolver](previous-versions/aspnet/hh969140)
 
 ### Registering services
 
@@ -116,6 +116,15 @@ public class HomeController : Controller
 }
 ```
 
+Within a request, a scoped set of services may be retrieved by a special extension method:
+
+```csharp
+var myService = HttpContext.Current.GetRequestServices().GetService(typeof(ISomeType));
+```
+
+> [!WARNING]
+> <xref:System.Web.HttpContext> implements <xref:System.IServiceProvider> so you may see extension methods to get services from it. However, it is not implemented in a way to retrieve any useful services from a registered container. You will see an error if you attempt to use it and you should instead use the `GetRequestServices()` extension method first.
+
 ## Logging
 
 The generic host integrates `Microsoft.Extensions.Logging`, providing a modern logging infrastructure for your ASP.NET Framework application.
@@ -191,6 +200,8 @@ var configValue = AppConfiguration.GetSetting("SomeSettings");
 var connStr = AppConfiguration.GetConnectionString("connection-string-name");
 ```
 
+This will work on both ASP.NET Core and ASP.NET Framework applications that are referencing `Microsoft.AspNetCore.SystemWebAdapters` and will provide access to the current `IConfiguration`.
+
 ### Using options pattern
 
 The options pattern provides strongly-typed access to configuration sections: