Improve auth state provider guidance for BWAs

[PMcVries]

Description

Following the documentation I came across an issue configuring authentication and authorization for a Blazor Server app. The [Authorize] attribute kept redirecting to (I assume) my authentication scheme's fallback path instead of just displaying the fallback message "Not authorized. I used Cookie Authentication. Neither role-based, policy-based nor the default policy was recognized.
After some research I've found this workaround to fix this problem. https://github.com/dotnet/aspnetcore/issues/52317#issuecomment-1830673284

The workaround just inserts a middleware step and assumingly skips the redirections issue.

Please add this information into the documentation since it seems to be a recent problem since the introduction of .NET 8.
Thank you!

Page URL

https://learn.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-8.0#additional-resources

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/blazor/security/index.md

Document ID

1247ee64-fbc9-ce29-0710-f6e59380f5ee

Article author

@guardrex

[PMcVries]

@AdmiralSnyder fyi

[guardrex]

Thanks, @PMcVries ... I'll get on this tomorrow or early next week.

dotnet/aspnetcore#52317 (comment)

[guardrex]

I don't think we'll document the workaround. We're more interested in Surayya's suggestion ...

it's better if you perform the authentication within the ASP.NET Core auth system and your authentication state provider only takes care of reflecting that state.

I think the one she's referring to this this one ...

https://github.com/dotnet/aspnetcore/blob/main/src/ProjectTemplates/Web.ProjectTemplates/content/BlazorWeb-CSharp/BlazorWeb-CSharp/Components/Account/PersistingRevalidatingAuthenticationStateProvider.cs

That one, along with the other auth state providers, is covered in the article, but it's only a quick mention and cross-link to the reference source.

I'll use this issue to both call out the behavior and clarify that these project template-based approaches are what the PU recommends.