This works for me
if (isset($_SERVER['HTTPS']) &&
($_SERVER['HTTPS'] == 'on' || $_SERVER['HTTPS'] == 1) ||
isset($_SERVER['HTTP_X_FORWARDED_PROTO']) &&
$_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https') {
$protocol="https://";
}
else {
$protocol="http://";
}