How to download paid files from sites for free?

Question

JavaScript

Hello.
I heard several times that you can download paid files (books, music, videos, etc.) for free, somehow correcting the code in the console.
How is this done, and how can you protect your project from such "hacks"?

Answer 1

Validate incoming data on the server, not just the client.
Use csrf token

Answer 2

Make a token on the backend that is tied to a specific user, ip, time. When downloading, check it, if everything is fine, give the file to the client through a script (in php this is readfile())