Users can sign up with GitHub and use it to sign in to the dashboard, but not the CLI.
See APPTS-7024 for the discussion.
We need to investigate if signing in to the CLI with GitHub is possible (with a good UX).
If so, and Studio (TISTUD-8507) is able as well we need to implement it. If not, then we should remove the ability to sign up with GitHub in the first place.