django authentication without a password

I'm using the default authentication system with django, but I've added on an OpenID library, where I can authenticate users via OpenID. What I'd like to do is log them in, but it seems using the default django auth system, I need their password to authenticate the user. Is there a way to get around this without actually using their password?

I'd like to do something like this...

user = ... # queried the user based on the OpenID response
user = authenticate(user) # function actually requires a username and password
login(user)

I sooner just leave off the authenticate function, but it attaches a backend field, which is required by login.