Thank you for the complement!
In situations like these we create an extra model for "public" users which we can manage in Skyline as a content models. Then we define a setting which points to a page. In the pages controller we check if the visitor tries to access this specific page (or any of it's sub-pages) and redirect the user to a login page if he/she hasn't logged in yet.
Does that help?
Cheers,
Flurin Egger