public function getAuthorizationHeader(
        array $headers,
        $url,
        array $queryParams,
        $httpMethod
    ) {
        $signature = $this->computeSignature(
            $headers,
            $url,
            $queryParams,
            $httpMethod
        );

        return 'SharedKey ' . $this->accountName . ':' . base64_encode(
            hash_hmac('sha256', $signature, base64_decode($this->accountKey), true)
        );
    }