I have a client that wants to send a JSON string full of data to me, have me run a process on it, then send it back.

I figured I'd set up a NGINX server and have the client use a GET or POST URL with the JSON string in it, but I'm having trouble figuring out how to have NGINX pass the JSON string over to my process? Ideally it would parse the string into a .txt file or something, but I have no idea how to make it do that.