'Controls whether the given User may log in. This is a policy setting,
independent of end-user authentication. This default behavior is to
allow login by active users, and reject login by inactive users.
If the given user cannot log in, this method should raise a
``forms.ValidationError``.
If the given user may log in, this method should return None.'

def confirm_login_allowed(self, user):

    if (not user.is_active):
        raise forms.ValidationError(self.error_messages['inactive'], code='inactive')
