Download with security

Hello there, I got to make a page where after a user login, he can download whatever files he want (the available for his access level). My question is where do I make the security access? 1 - On the server - Apache. It would be very difficult to create each user access whenever a new user appeared. 2 - Programming - Php. But in this case there would be a problem, since I can't control the file links. After someone downloaded the file, he could download it again without making any type of authentication. How can I make the link available only after login? Thank you very much for your time, Rui