Acces to folder from backend

Hello,

Is there a way to acces a folder from the backend?
I have a php application that has nothing to do with the wordpress site but it has to run on the same server. (ie http://www.site.com/application is the path for the application) Is there a way to use the backend to scheck if someone that is trying to acces the application directly is logged in in wordpress, if not redirect so the user can log in and make the application accesible from the backend without making a plugin to do so.