When setting up the server for local development if the developer forgets to set or incorrectly sets the MUSICBRAINZ_CLIENT_ID or MUSICBRAINZ_CLIENT_SECRET values in config.py, they will get a confusing login page.

This is a browser behavior that happens when a 401 or 403 is returned on a login page iirc, we cannot do much to modify it but we can document it in the docs.

If you click on cancel you are taken to a more relevant error page which might be helpful in debugging.

A note under update config.py probably makes sense.