Blazor WebAssembly debugger fails when anonymous auth is false

[JoelW187]

Describe the bug

When launching a hosted Blazor WebAssembly application under the IIS Express profile in Visual Studio 2019 the debugger won't launch if the anonymousAuthentication setting (under iisSettings in launchSettings.json) is false.

To Reproduce

1. In VS2019 create a new "Blazor WebAssembly App" with the "ASP.NET Core hosted" ticked. The template automagically adds windowsAuthentication: true and anonymousAuthenticaion: true. Also, the inspectUri strings are added to the launchSettings.json file to enable debugging.

2. Set a breakpoint in a client razor file (such as Counter.razor) and run the app. The app will launch normally and break at the breakpoint when it's reached.

3. In launchSettings.json, change anonymousAuthentication to false and launch the app. The browser hangs for 60 seconds and then VS2019 throws an exception:
   

(It doesn't matter what the value of windowsAuthentication is, as long as anonymousAuthentication is false the debugger fails to load).

Exceptions (if any)

Further technical details

• ASP.NET Core version 3.1.4
• Visual Studio 2019
• Blazor WebAssembly packages version 3.2.0

c:\junk>dotnet --info
.NET Core SDK (reflecting any global.json):
Version: 3.1.300
Commit: b2475c1295

Runtime Environment:
OS Name: Windows
OS Version: 10.0.17763
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.300\

Host (useful for support):
Version: 3.1.4
Commit: 0c2e69caa6

.NET Core SDKs installed:
2.1.509 [C:\Program Files\dotnet\sdk]
2.1.511 [C:\Program Files\dotnet\sdk]
2.1.512 [C:\Program Files\dotnet\sdk]
2.1.513 [C:\Program Files\dotnet\sdk]
2.1.514 [C:\Program Files\dotnet\sdk]
3.0.101 [C:\Program Files\dotnet\sdk]
3.1.201 [C:\Program Files\dotnet\sdk]
3.1.300 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.16 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.16 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.16 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

[javiercn]

@JoelW187 thanks for contacting us.

This is likely due to the proxy failing to connect to the host due to Windows auth being on. I believe this will go away once we move the debugger proxy to a separate process.

/cc: @captainsafia

[mkArtakMSFT]

Thanks for contacting us.
This will indeed be resolved after we have #21466