TYPO3 Core

This is just about the class property, right?

Yes, I came across it while searching for deprecated functions to be removed in 6.1. This one was not that easy, so maybe someone more experienced in the login part can take care of this one.

So we won't have ('normal', 'challenged', 'superchallenged') anymore? Was it decided to only keep "superchallenged" from now on?

Does not seem like security_level is mentioned in any documentation (at least not in the Security Guide); no need to update any docs for this change.