public function submit(RequestParameters $params)
    {
        $handle = $this->curl->init($this->siteVerifyUrl);

        $options = array(
            CURLOPT_POST => true,
            CURLOPT_POSTFIELDS => $params->toQueryString(),
            CURLOPT_HTTPHEADER => array(
                'Content-Type: application/x-www-form-urlencoded'
            ),
            CURLINFO_HEADER_OUT => false,
            CURLOPT_HEADER => false,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_SSL_VERIFYPEER => true
        );
        $this->curl->setoptArray($handle, $options);

        $response = $this->curl->exec($handle);
        $this->curl->close($handle);

        if ($response !== false) {
            return $response;
        }

        return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
    }