I\'m building a site where registered users can upload files. Those files are then served via Apache. Only users who are logged in should be able to access those files.
The usual way to do this is to pass back a special header to the web server.
You can do it with nginx using x-accel-redirect as in this Django snippet.
For Apache, it should be pretty similar using the mod_xsendfile module (discussion and examples on Django users mailing list).
If you have freedom to switch from Apache to lighttpd, then the most straightforward solution would be to use mod_secdownload which would do exactly what you want, that is, provide application authentication while serving the actual files via web server.
However if you are stuck with Apache, then I suggest mod_auth_token, here they mention PHP but you can generate the token in Python or any other language. Using mod_auth_token you will be able to generate the token in your application, and then have web server serve the static file utilizing that token.