public function getSignedCookie($url = null, $expires = null, $policy = null)
    {
        if ($url) {
            $this->validateUrl($url);
        }

        $cookieParameters = [];
        $signature = $this->signer->getSignature($url, $expires, $policy);
        foreach ($signature as $key => $value) {
            $cookieParameters["CloudFront-$key"] = $value;
        }

        return $cookieParameters;
    }