A number of people have asked about getting my.openHAB to support proxying ssh so users can get to their Pis from outside their network without punching a hole in their firewall. As explained in those threads, this is not really something that the binding is designed to do.
I just ran across this little tool called Dataplicity which appears to provide an ssh like proxy to your Pi. All you need is to install their server on your Pi, make sure the Pi has internet access, and a web browser and their cloud service proxies your browser window to your Pi, giving you a command shell.
I don’t use this nor do I have a plan on using it (I’m happy with my ssh with certs approach) and I haven’t really delved deeply into how it works. Caveat emptor.