Add ability to return a 401 response on wrong basic auth for forward auth proxy provider

[sanzoghenzo]

Is your feature request related to a problem? Please describe.

I've correctly set up authentik domain level forward auth provider to secure some web apps behind traefik. I've developed an headless client that uses a service account and basic auth to connect to one of the services; everything works well, but if I specify wrong credentials in the basic auth, I still get a 200 response code because, as stated in the documentation, "If the received credentials are invalid, a normal authentication flow is initiated", so I get the login page as response.

Describe the solution you'd like

Return a 401 response on invalid basic auth credentials, especially with service accounts.