This is a continuation of #3346 based on the advise of https://codeberg.org/forgejo/forgejo/issues/1452#issuecomment-14591307. fixes: #1452 docs: https://codeberg.org/forgejo/docs/pulls/1938 Extends the `oauth2_client` `USERNAME` setting to be able to use the `preferred_username` claim. Co-authored-by: thepaperpilot <thepaperpilot@gmail.com> Co-authored-by: Anthony Lawn <thepaperpilot@gmail.com> Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12504 Reviewed-by: Gusted <gusted@noreply.codeberg.org>