title: Prevent user's from logging in if they are suspended
body: <p>I am using loopbackjs with passport and facebook-auth to acquire users. This works well, but I need to prevent users from logging in if they have been suspended. I have no idea how to implement this. Initially I thought of simply moving the entire user record to a different collection, but that causes the obvious problem of not being to stop the user from re-registering themselves...  so how can this be implemented.</p>