Require/generate --auth username:$(random password...) by default

Considering the power of the tunnel that chisel creates (it gives access to all localhost ports by default, without authentication!) it would be prudent to force users to supply some sort of credentials by default when starting the chisel server.

When starting the server without --auth, it should autogenerate some credentials.

Alternatively, maybe there could be a simpler way to specify authorization rules than the users.json file.
I think whiltelisting should be used for ports, so that by default, no ports are accessible.

We can use chisel to ssh into servers from within restrictive networks that only allow http traffic. But for that purpose, we only need access to port 22 on the server running chisel server, not all the rest of ports.

Start by reviewing the server's --auth startup behavior and how users.json currently expresses authorization. Define whether the intended result is autogenerated credentials, simpler authorization rules, port whitelisting, or a combination, then verify that unauthenticated servers expose no ports beyond the documented default.