private function prepareProxy(&$opt, $url)
    {
        $scheme = parse_url($url)['scheme'];
        if ($scheme === 'http' && (!empty($_SERVER['HTTP_PROXY']) || !empty($_SERVER['http_proxy']))) {
            $proxy = !empty($_SERVER['http_proxy']) ? $_SERVER['http_proxy'] : $_SERVER['HTTP_PROXY'];
        }

        if ($scheme === 'https' && (!empty($_SERVER['HTTPS_PROXY']) || !empty($_SERVER['https_proxy']))) {
            $proxy = !empty($_SERVER['https_proxy']) ? $_SERVER['https_proxy'] : $_SERVER['HTTPS_PROXY'];
        }

        if (!empty($proxy)) {
            $proxy = str_replace(['http://', 'https://'], ['tcp://', 'ssl://'], $proxy);
            $opt['http']['proxy'] = $proxy;
        }
    }