Thankyou -- Scott Klement!
HTTPAPI (LIBHTTP) on IBM i is the bomb. Luckily I am not boarding a plane at the moment, so I can use that kind of language without getting strip searched by some burly TSA agents.
Firstly, I have never met Mr. Klement but (like almost every IBM i Developer out there) have read many of his excellent articles about programming and tinkering with IBM i systems. Secondly, the man is a genius and I owe him a very large beer. After spending far too long investigating various techniques to get my IBM i system to talk to an external website (Authorize.net in this case) and being led down many wrong roads... I stumbled across scott's collection of open source RPGLE programs called HTTPAPI.
In Scott's words:
Download HTTP API source:
This is an RPG IV service program that uses socket calls to implement the HTTP 1.1 protocol. The HTTP protocol is the data transfer protocol that is used to transfer documents over the World Wide Web.
This service program can, optionally, also do "https" (HTTP over SSL) requests to an SSL-enhanced web server.