Mixed applications

I need to create two applications on the same database. The first one I created a security module. The second application must respect the authorisation, but does not contain the maintenance functions. I can create a control app to let the user login. How can I let the other apps of the second application respond to the authorisation access table? If I set the appropiate checkbox what will happen? This second application does not ‘know’ that there are security tables? Or does it?
What is the best approach of buildingthis: two projects or one?