It pretty much only accomplishes what you can already do with a
normal SSH client. The difference is that keys are generated on
the fly by the server and transmitted for the client to use for
the tunnel.
I had been moving in the direction of implementing a custom SSH
server in golang. That would be pretty easy if using a custom
application protocol, but I want to support tcpip-forward which
looks like it would be a lot more work. It also would be nice to
support generic CLI clients like OpenSSH.
The point of using SSH in the first place is that it's known to be a
solid tunneling solution. To that end, I've decided to rely on
OpenSSH for now, since that program may have tunneled more bits than any
other since the dawn of time. This requires a bit of hackery to generate
SSH keys and place them in authorized_keys (as well as shipping the
private key to the client), but I think this will work well for now.
Plus OpenSSH is already installed on pretty much every server
I'd expect to run boringproxy.
Turns out SSH has robust semantics for opening generic channels.
Looks like I'll be able to set up tunnels without ever needing to
forward ports on the server, since I can connect the channels with
a custom protocol.
Of course I'll eventually want to support generic SSH clients, but
this makes starting much easier.
