def get_or_create_user(self, username, ldap_user):
        """
        This must return a (User, created) 2-tuple for the given LDAP user.
        username is the Django-friendly username of the user. ldap_user.dn is
        the user's DN and ldap_user.attrs contains all of their LDAP attributes.
        """
        model = self.get_user_model()
        username_field = getattr(model, 'USERNAME_FIELD', 'username')

        kwargs = {
            username_field + '__iexact': username,
            'defaults': {username_field: username.lower()}
        }

        return model.objects.get_or_create(**kwargs)