Single Sign On for modx external authentication super handy if you're authenticating with some other project and just need to assign privileges to a session.

modx external authentication.php

<?php
//require 'modx/assets/kint/Kint.class.php';
 
require_once __DIR__ . '/modx/config.core.php';
require_once MODX_CORE_PATH.'model/modx/modx.class.php';
$modx = new modX();
$modx->initialize('web');
$modx->getService('error','error.modError', '', '');

$user = $modx->getObject('modUser', array('username' => 'levi'));
$user->addSessionContext('mgr');

//dd($user->get('username'));