Is it possible to ssh through HTTPS without a proxy, using normal tools, like ThinVNC does?
The network is closed from the outside world, only access to websites is allowed, and that's only through a proxy that blocks the usage of other proxies.
It is possible, I've done it by myself by changing the listen port of my ssh server in /etc/ssh/sshd_conf from 22 to 443 (HTTPS). Be sure that your server is not already listening on this port before.
Don't forget to restart the sshd service after your modification.
Also, use the -p option when you're using the ssh client to set the port.
httptunnel
but it doesn't support HTTPS.