Mobile App Redirect when logged/not logged in

Still going with my mobile app questions

I can’t use the App Connect Page protection since I’m not on a php page in the mobile app. So my reasoning is to check if user is logged in by running a server action when app opens(1st page - login) to check if they are logged in. If server actions runs successfully, redirect using app connect browser. If not successful, stay on current/login page.

But I do not know how to make the server action run unsuccessful when not logged in. Could one use throw errors to get this to work…?

Any other ideas also welcome besides redirect using browser function on success of server action.