I want to add a Google Checkout button to a custom-built ASP shopping cart. The cart currently has a PayPal button, but my client wants to also offer Google Checkout as an option to buyers.
Since the page with the checkout buttons is not secure (no SSL), I just want to post the amount to Google, have Google process the charge (like Paypal) and return the customer back to the site. This would all work very much like PayPal's IPN system. On return to the site, the order ID number must be passed back (in the URL or as a form field) so the database can be updated to mark the order as paid.