I have two linux machines behind NAT routers which I do not control. I want to use a third, publicly accessible server (some cheap vps) to act as a middle-man, where the two endpoints can both connect.
I could easily accomplish this by making the VPS the openvpn server, but then it would have access to all the decrypted traffic between the endpoints. How can I configure it so that the middle-man vps does not have access to the key (I plan to use shared keys for this).