Permissions Through A Browser

[Azathoth]

I'm running a php flash content server, and if I'm not mistaken, users viewing my files fall into the "Other" permissions group.

I was wondering if through my php code (or any other way really) I could allow users to fall into the "Group" or "Owner" permissions group.

The problem is that I want people to be able to view my content if they're logged in (their url when viewing a flash file looks something like

http://flashserver.com/showfile=file1),

but not if they just type an actual location into their browser (such as

http://flashserver.com/content/movie.swf).

Any insight would be greatly appreciated.