Usually the password is something stupid and it's just trying to keep out the mentally ill or people who overdose on drugs in there.

They try everything in Chicago, from 12345 to blue lights in the bathroom to make it harder for people to find a vein.

Many cities, like San Francisco, resorted to pay toilets years ago. The idea is that if you just lock everyone out who doesn't have a couple bucks in their pocket, the stalls will be cleaner and with fewer syringes.