$proxy = '1.2.3.4:60000';
$query = curl_init('https://ip.oxylabs.io');
curl_setopt($query, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($query, CURLOPT_PROXY, "http://$proxy");
curl_setopt($query, CURLOPT_PROXYUSERPWD, "$username:$password");
$output = curl_exec($query);