protected function validateRequest()
    {
        $data = $_POST;
        $url = $this->url;
        $signature = $_SERVER['X-Plivo-Signature'];
        $authToken = $this->authToken;

        if (!$this->plivo->validate_signature($url, $data, $signature, $authToken)) {
            throw new \InvalidArgumentException('This request was not able to verify it came from Plivo.');
        }

        return true;
    }