A couple of years ago I used Zipato. I could make virtual sensors in their cloud that were accessible by an “impossible to guess URL” (two GUIDs combined).
The Zipato box would have a socket connection open against the cloud and get immediate notification when the virtual sensor got a new state. In that way, there was no need for open ports to the outside because the box would pull the state change from the cloud whenever it was notified. At least I think this was the way it was working 
Is there any way to do similar things with HA and HA cloud? I think I read about something similar but I am unable to find it now.
I don’t want to open any ports from the Internet, but am a little hesitant about security by obscurity too (hard to guess urls).
Any thoughts?