I would keep App Page as your “base” form where you add/remove forms as components to some card/column panel.
The Login/Logout button would then be a single button that changes text/executes different code pending on a user being logged in or not. (by changing the click event or checking the text on the button)
In App Page you can check if a user is logged in, if they are not, then you route them to a Not Logged in Page else the Landing Page.
For routing I would look into this library: