Sulu CMF: Access control to parts of the website

I try to create a password protected area of a webpage using Sulu CMF and have problems making it work properly.

I followed this guide: https://docs.sulu.io/en/2.5/cookbook/user-context-caching.html

As a consequence, when activating permissions for a subpage in the admin, the page is not displayed in the navigation anymore, which is good. But I am still able to display the page using the corresponding url in the browser, instead of beeing redirected to the login page.

What am I missing?