StartupHook is preventing launching of child .NET processes

[NCarlsonMSFT]

Similar to the issue with Hot Reload (dotnet/runtime#58000) when StarHostAction in the Azure Functions CLI sets DOTNET_STARTUP_HOOKS it should be cleared in StartupHook to prevent all child processes from inheriting the environment variable and failing to run.

This is currently blocking the ability to use the VisualStudioCredential from Azure.Identity in some scenarios as it relies on starting a child process.

[fabiocav]

Thanks @NCarlsonMSFT . This is reasonable and we'll have this reviewed.

In the meantime, you can workaround the issue by clearing that startup hook reference in debugging scenarios (or always, if you always want to suppress that behavior)

[jsheetzmt]

Also interested in this as we are trying to use VisualStudioCredential for AAD authentication with isolated functions + Docker containers.

This is the error we are getting:

[2023-05-08T15:58:08.134Z] - Process "/TokenService.Proxy/TokenService.Proxy" has failed with unexpected error: Unhandled exception. System.ArgumentException: Startup hook assembly 'Microsoft.Azure.Functions.Worker.Core' failed to load. See inner exception for details.
[2023-05-08T15:58:08.134Z]  ---> System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Azure.Functions.Worker.Core, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

[NCarlsonMSFT]

@jsheetzmt: I've updated my sample to include an Isolated Azure function with a work-around for this bug: https://github.com/NCarlsonMSFT/VisualStudioCredentialExample/blob/master/FunctionAppIsolated/Program.cs

[jsheetzmt]

Thanks @NCarlsonMSFT, that did the trick :)

[fabiocav]

Adding context to the issue on the file that would need to be modified to handle this: https://github.com/Azure/azure-functions-dotnet-worker/blob/main/src/DotNetWorker.Core/StartupHook.cs