[Twisted-web] Guard

[orbitz]

I'm trying to write the login portion of a webapp using guard.  I 
understand the checker side of things. I'll be using a database as the 
backend, and checking against it doesn't sound hard. The issue I'm 
having though, is that my authentication depends on 3 variables. A 
username, password, and department.  I'm not sure what I have to do to 
get these 3 things into the credential in order to authenticate. Is 
there a class I have to subclass and then override a method for or what?

Thank you.