Some time ago, we made this fix to external authentication – https://github.com/discourse/discourse/pull/13706. We didn't address Discourse Connect (https://meta.discourse.org/t/discourseconnect-official-single-sign-on-for-discourse-sso/13045) at that moment, so I wanted to fix it for Discourse Connect as well.
Turned out though that Discourse Connect doesn't contain this problem and already handles staged users correctly. This PR adds tests that confirm it. Also, I've extracted two functions in Discourse Connect implementation along the way and decided to merge this refactoring too (the refactoring is supported with tests).