public function storeSecretKey($keyId, $secretKey)
    {
        if (is_null($keyId) || strlen(trim($keyId)) == 0) {
            throw new UnexpectedValueException("keyId is required");
        }
        if (is_null($secretKey) || strlen(trim($secretKey)) == 0) {
            throw new UnexpectedValueException("secretKey is required");
        }
        $this->secretKeys[$keyId] = $secretKey;
    }