Prerendering Blazor WASM .NET 5 app with authentication throws error

[ChristianWeyer]

I have a Blazor WASM application using OIDC authentication (based on this https://docs.microsoft.com/en-us/aspnet/core/blazor/security/webassembly/standalone-with-authentication-library?view=aspnetcore-5.0&tabs=visual-studio). This works fine.

Now, when I add WASM prerendering (based on this https://docs.microsoft.com/en-us/aspnet/core/blazor/security/webassembly/additional-scenarios?view=aspnetcore-5.0#support-prerendering-with-authentication), then it no longer works. I get a strange behavior after the app loads and 404 errors. The redirect after the login then also hits a 404.
In fact, every route is giving a 404... hm...

Here is a small demo video:

This is the demo code:
https://github.com/thinktecture/blazor-webassembly-demo/tree/prerender

.cc @guardrex
dotnet/AspNetCore.Docs#20696

[guardrex]

I'll update the <app> to <div id="app"> on dotnet/AspNetCore.Docs#20698 and dotnet/AspNetCore.Docs#20737 PRs and then followup later with a new PR for anything else that we need to do for this scenario in 5.0 docs.

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