[JENKINS-70035] Use User.getById() instead of User.get()

[Kevin-CB]

You can find more information in JENKINS-70035

I had to adapt LdapMultiEmbeddedTest#when_first_is_unavailable_and_ignorable_and_login_on_second_then_login & LdapMultiEmbeddedTest#when_first_is_wrong_and_ignorable_and_login_on_second_then_login to match AuthenticationServiceException and not UserMayOrMayNotExistException2 because they were not thrown anymore.

As I did not fully understand their uses, I would ask you to review this part carefully to make sure that I didn't broke them.

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[dwnusbaum]

Sorry, but I do not remember if the specific exception type here is important (I would assume it does not matter though, and I doubt that the multi-server mode is used very frequently anyways). What is the full stack trace in the logs before and after the change? Maybe the only difference is that there is a new outermost exception?

[jtnord]

UserMayOrMayNotExistException2 seems important as it is used to say "I can not tell you that this users exists. or not" and as such can allow the use of a token (wheras another excpetion would be treated as the form - this user does not exist).

At the very least I think some manual testing with user impersonation needs to occur when the server is down (before and after this change)