HTTPS server for SAP Ariba Network with cXML

I know this may be borderline WEB400 mailing list but the current
situation is more general about the direction to start and nudging toward
RPG backend.
The SAP Ariba Network is supposed to be one of the largest B2B networks
and has an option for cXML via HTTPS as a new EDI trading partner. We are
the seller and they are the buyer. FTP is not an option under SAP Ariba
Network. Not sure of the software options available. We could always go
the easy VAN (Value Added Network) route like many of our rather small
trading partners but this buyer suggests using HTTPS with cXML for added
value. Even though there can be some large costs with the network, the
trading partner noted that they would foot the bill for the SAP Ariba
Network. We just have to decide our option. We also have a much larger
buyer that is requesting us to be in their pilot for this exact same SAP
Ariba Network but that hasn't gone anywhere for awhile. I also like that
cXML is supposed to have standardized formats for Purchase Order,
Confirmation, ASN, Invoice. They send the PO to our server (POST request
with response), we later send the confirmation, ASN, and invoice to their
server.

Has anyone implemented an HTTPS server with SSL with RPG as the resource
using the SAP Ariba Network with cXML? I don't think we would be
utilizing PunchOut. We already have a partner where we receive XML
documents via SFTP, parse, and send the ASN and invoice via a web service
to their server. I make use of the HTTPAPI to send the XML to their web
server. Our EDI software takes care of parsing and mapping even though we
could use RPG but our software support said they don't have anything
really for HTTPS. At first thought, Scott Klement's documents about using
RPG as a resource with handling request response along with HTTPAPI as the
client seemed in scope. Then, there was mention in cXML documentation
about a POST request to determine cXML version and capabilities along with
predetermined response codes. That got me thinking, maybe this is
something I cannot develop in house to satisfy their standards and maybe
should go the software route? Maybe that free solution just turned into a
behemoth? Any suggestions or experiences?

Thanks,
Craig Strong