private function signatureIsValid($httpMethod, $url, $publicKey, $privateKey, $timestamp, $signature) {
        // Generate data for the HMAC
        $data = $httpMethod . '|' . $url . '|' . $publicKey . '|' . $timestamp;

        // Compare
        if ($signature === hash_hmac($this->algorithm, $data, $privateKey)) {
            return true;
        }

        return false;
    }