SSH

SSH is great.

SSH is susceptible to brute-force attacks. pam_abl is one solution.

Public Key Authentication

See SSH Public Key Authentication.

Tunneling

SSH can do tunneling.

See https://blog.linuxnet.ch/automatic-tunnels-with-xinetd-and-netcat/ for a way to do tunneling automatically. It uses xinetd to bind a port to a program.