silverstripe-framework/tests/php/Security/SecurityTest/SecuredController.php

<?php

namespace SilverStripe\Security\Tests\SecurityTest;

use SilverStripe\Control\Controller;
use SilverStripe\Dev\TestOnly;
use SilverStripe\Security\Permission;
use SilverStripe\Security\Security;

class SecuredController extends Controller implements TestOnly
{
    private static $allowed_actions = ['index'];

    public function index()
    {
        if (!Permission::check('ADMIN')) {
            return Security::permissionFailure($this);
        }

        return 'Success';
    }

    public function Link($action = null)
    {
        return Controller::join_links('SecurityTest_SecuredController', $action, '/');
    }
}