static function fromSuccessResponse($success_response, $signed=true)
    {
        $obj = new Auth_OpenID_AX_FetchResponse();
        if ($signed) {
            $ax_args = $success_response->getSignedNS($obj->ns_uri);
        } else {
            $ax_args = $success_response->message->getArgs($obj->ns_uri);
        }
        if ($ax_args === null || Auth_OpenID::isFailure($ax_args) ||
              sizeof($ax_args) == 0) {
            return null;
        }

        $result = $obj->parseExtensionArgs($ax_args);
        if (Auth_OpenID_AX::isError($result)) {
            #XXX log me
            return null;
        }
        return $obj;
    }