on the other hand, its SQL backend modules insist on fetching a password and comparing them using their own functionality and there's no way to get to the the user's typed password into a custom query.

That means that there's no way to authenticate users if you use a password encryption scheme not supported by the bundled modules (like bcrypt for example)

I am not sure why I didn't realize that sooner, but that's awesome, thank you for pointing that out.