How does programmatic access tie into the desire for a login form?

I would like to keep files with “private” information protected from public access, but I would like to access them from a script. An example: i wrote a karaoke application to use with my friends, they have to go to a webpage and select the songs they like, and then the karaoke app connects to the server to get the updated preference file. I would like that the users had a “nice login form” to select their songs, and then I’d like my karaoke app to easily download the file while still keeping it password-protected