Returns True if the group requirement (AUTH_LDAP_REQUIRE_GROUP) is
        met. Always returns True if AUTH_LDAP_REQUIRE_GROUP is None.

def _check_required_group(self):
        """
        Returns True if the group requirement (AUTH_LDAP_REQUIRE_GROUP) is
        met. Always returns True if AUTH_LDAP_REQUIRE_GROUP is None.
        """
        required_group_dn = self.settings.REQUIRE_GROUP

        if required_group_dn is not None:
            is_member = self._get_groups().is_member_of(required_group_dn)
            if not is_member:
                raise self.AuthenticationFailed("user is not a member of AUTH_LDAP_REQUIRE_GROUP")

        return True