private function addRequestAuth(&$curlOptions) {
        $username = $this->getOption(self::USERNAME_KEY);
        $password = $this->getOption(self::PASSWORD_KEY);
        if ((!is_null($username)) && (!is_null($password))) {
            $curlOptions[CURLOPT_USERPWD] = sprintf("%s:%s", $username, $password);
        }
    }