public function verifySignature(array $data)
    {
        $signedData = array_intersect_key($data, array_flip(self::$validResponseParams));
        ksort($signedData);

        $queryString = $this->buildQueryString($signedData);
        $signature = base64_encode(hash_hmac('sha1', $queryString, $this->clientSecret, true));

        return hash_equals($signature, $data['h']);
    }