B1 Integration with an external system: Secure Communication

as business needs, I have to setup our company's B1 system integration with an external system which outside our domain.

B1-B1iSN-External systems

(External system sends or receives transactions via EDI across the enterprises)

I think the prerequisite for establishing this integration is that the external system must have the access to our B1iSN server and vice versa.

I know that an external system integrated with B1 backend via B1if would preferHTTPS communication than HTTP for sensitive business data is transport through Internet. And HTTPS typically use SSL or TSL secure protocols to encrypt communications.

I can see that below link describes how to generate and install a SSL certificate for B1if.

http://scn.sap.com/docs/DOC-57709

My intention was that to let external system use HTTP asynchronous call to B1iSN.

http://<ip>:8080/B1iXcellerator/exec/ipo/<sysid>.inbound/com.sap.b1i.datasync.ipo/P61/P61.ipo/HTTPInbound

but I don’t know how can I enable a secure connection with HTTPS to B1iSN?

I would like to hear your suggestions for ways of secure communication?