When setting up a custom button at Paypal, you have the option under "Website Payment Preferences" to provide a link that Paypal will automatically redirect the user to upon successful completed payment.
Under the Payment Data Transfer you are given an "Identity Token". My presumption is that you can test for the presence of this identity token on your download page and either allow or disallow access to the product download based on whether (1) the token is correct and (2) the token came from the Paypal server (and not someone spoofing the token)
If anyone has some experience with interfacing with Paypal during a product download transactions, I'd really appreciate your input on how to do this.
I basically have a script that I've created to allow or disallow the streaming of the download file and I'm trying to fill it out with the Paypal challenge code.
if (this is an authentic request from paypal and payment has been confirmed)
{
//stream the file to the user. I have code for this.
}
else
{
//not a valid request, redirect to order page
}