fix(auth): check suffix correctly in domainAllowed
What does this MR do?
This MR fixes the check that is used to decide if a domain is an allowed domain, which was originally added in !94 (merged).
The correct check was suggested in this comment but the implemented version added in this commit added the "." in the wrong place.
I added some simple unit tests; however, I'm not very familiar with the mocking mechanisms used in GitLab Pages, so I would appreciate pointers to improve my tests.