Create a logged in session programmatically in XF2

get_authenticated_cookie.php

<?php
$userId = XXXX;
/** @var \XF\Entity\User $user */
$user = \XF::app()->finder('XF:User')->where('user_id', $userId)->with(['Profile'])->fetchOne();
if (!$user) { /* there's no such user */
    return;
}
$class = \XF::app()->extendClass('XF\Session\Session');
/** @var \XF\Session\Session $session */
$session = new $class(\XF::app()->container('session.public.storage'), [
    'cookie' => 'session'
]);
$session->start(\XF::app()->request());
$session->changeUser($user);
$cookieVal = $session->getSessionId();
$session->save();
// set the xf_session cookie, via codeigniter or whatever, to
$cookieVal;