Add a security code to http get request : I am searching a security function like this:
The user can put his paypal address and an amount of money(which he gained in my app) in my application, and I will recieve it with an http request on my server. Now this is really insecure, anyone with the http requesturl can send me payout data for himself. So what I need is something like a code generator that only my app can create this sort of code, and my php script checks if the code doesnt fit, it wont accept the request. I thougt about java encryption, to encrypt the amount of money. but anybody with the skills to generate a java encrypter can also create an url to send a whitedraw request I think?

I saw an app with this function, its called plus500 there you can whitedraw your money to a(your) paypal account, but I'm not that pro finding out how they do this feature securely.