public function setProxy(string $proxy_address, string $proxy_port = null, string $proxy_userpwd = null): void
    {
        $this->CURL_DEFAULTS[CURLOPT_PROXY] = $proxy_address;
        if ($proxy_port) {
            $this->CURL_DEFAULTS[CURLOPT_PROXYPORT] = $proxy_port;
        }

        if ($proxy_userpwd) {
            $this->CURL_DEFAULTS[CURLOPT_PROXYUSERPWD] = $proxy_userpwd;
        }
    }