cfml

Since it's a JavaScript sdk, it would all happen on the client side via functions in that JS file that gets included by the script tag… naturally there would be no CF code as CF is a server side language 

That all happens via ajax requests to the Amazon servers 

Try turning on your browser developer tools and watch the network activity when you go through the checkout process 

Hmmm, slacking on my phone so that is a bit hard to read and follow. Perhaps they are hiding the voodoo magic in some clever way

Maybe someone who is on an actual computer can look and chime in

Yeah, graphic indicates it all happens on Amazon hosted stuff