How about creating your own authentication system using your web server? Just put your files in some protected directory that requires authentication. Then you can add and revoke access as needed.

Additionally, you won't have to give someone a script to download the files - they can just use their web browser. But if you need to script it, you can use LWP or wget or curl or ... In any case, the credentials you put in the script will only give access to the files in the protected directory.