Admin Module returnUrl

In protected/modules/admin/controllers/DefaultController.php I have:

if($model->validate() && $model->login())


I have enabled authentication on action: /admin/user/index

So when a (non-authenticated) user navigates to this URL, they are presented with the module login page. Everything fine so far.

Now when the user logs in successfully, they are then redirected to /site/index

This is wrong. They should be redirected to the originating URL (/admin/user/index)

How can I enable this? Do I need to set some property in AdminModule.php?