Guide to SSH Reverse Tunneling
pinggy.io
pinggy.io
ssh -R [bind-address:[remote-port]:][hostname]:[port] [user]@[remote-host]
Not specifying a bind address binds to all. Using localhost limits exposure.And repeated use of -R ... for multiple reverse port forwards (might not have been mentioned, I didn't see it).
They don't mention how pinggy does what it does, and I'd be very cautious to use closed 3rd party binary for such a security needed tool. Edit: There's a FAQ https://pinggy.io/help/#faq