you can limit which members of orgs/teams on github.com can login/sign up

--oauth2-github-allow-signups                Specifies whether new users can sign up
                                                   with GitHub.
                                                   Consumes $CODER_OAUTH2_GITHUB_ALLOW_SIGNUPS
      --oauth2-github-allowed-orgs stringArray     Specifies organizations the user must be a
                                                   member of to authenticate with GitHub.
                                                   Consumes $CODER_OAUTH2_GITHUB_ALLOWED_ORGS
      --oauth2-github-allowed-teams stringArray    Specifies teams inside organizations the
                                                   user must be a member of to authenticate
                                                   with GitHub. Formatted as:
                                                   <organization-name>/<team-slug>.