For a forum, or the whole forum? There is a per forum require password option in the edit forum options screen in the Admin CP, but for a whole forum pass, maybe put the forums inside one forum and make that password protected?
I want to use a forum pass, because sb from competitive forum stolen admin account with unrestricted acces to important forums... I set up pass for ACP and he couldn't use it. So I had an idea to set passwords for important forums...
But you said "there are often better ways to get the same result". What do you mean?
If someone gained access to an admin account, your response should not be to add more passwords to forums, but to ensure that this account is not used/abused anymore.