public static function setSigningKey($keyPairId, $signingKey, $isFile = true)
        {
            self::$__signingKeyPairId = $keyPairId;

            if ((self::$__signingKeyResource = openssl_pkey_get_private($isFile ? fgc($signingKey) : $signingKey)) !== false) {
                return true;
            }

            self::__triggerError('S3::setSigningKey(): Unable to open load private key: '.$signingKey, __FILE__, __LINE__);

            return false;
        }