Authentication Handler as an Endpoint

Now that almost everything (Controller, RazorPage, SignalR Hub, HealthCheck, Grpc) in ASP.NET Core is becoming an Endpoint, I'm curious is there a plan to make [authentication handlers](https://github.com/aspnet/AspNetCore/blob/62351067ff4c1401556725b401478e648b66acdc/src/Security/Authentication/Core/src/AuthenticationMiddleware.cs#L45) into endpoints?

Start with the linked AuthenticationMiddleware.cs implementation and the issue's comparison with controllers, Razor Pages, SignalR hubs, health checks, and gRPC endpoints. Clarify whether authentication handlers should expose the endpoint model and what behavior or API is expected; done requires an agreed design and scope, since the issue currently asks only whether there is a plan.

Written by the indexing model from the issue text.