Ok, thanks for the clarifications. I think we should have reviewed Sign in to GitHub · GitHub to make sure there’s no use case that will break (for error handling). It’s almost sure that something will get broken but I agree that the probability is low.
It should be documented in Release Notes for XWiki 15.0-rc-1 (XWiki.org) ofc.
Changing my opinion to -0 (which is not blocking it).
Thanks