google authentication does not work / no other way to add a user?

After installation (current Distro, installation with docker compose), I need to log in. The proposed way is using the google-account. However, this does not work.
There is the "error 400". Based on the google page, there is a problem with the authentication solution used on the webpage?

Looking for other ways of adding users, I found in the documentation a solution with an add_user-file; which does not exist?
Do I have to write it? And if so, which fields are required?