I have already an application which generates a RSS feed for a database of products. I need to add to this RSS feed the html code for each item so that it complies with Google Checkout Button.
Each item is a product in my database and each needs to get a customized button form code - the steps involved will be
Create a checkout the item as an XML structure.
Create a signature for the shopping cart using the HMAC_SHA1 function.
Base64-encode the cart.
Base64-encode the signature.
Put the cart and signature into a Google Checkout button form.
This is exactly the process Google uses to create checkout buttons, but Google only allows this done by a human operator, I need this automated. Sample code at [url removed, login to view]