只要先有require config.php，再global $USER，則可利用$USER->xxxx取得mdl_user內的各欄位值，含自訂的欄位亦可！

<?php
require('path/to/config.php');
require_login();
global $USER;
$userid = $USER->id;
echo $userid;
?>

Reference: How to get user id of current user in moodle?