You can’t, *however* there is a checkbox under preferences of “require remote login (SSH)” that accomplishes something similar.
Basically if you check this, then vine won’t “listen on port XXX” it’ll only list on localhost’s port XXX” (XXX is whatever port it says in the preferences).
with “require remote login (SSH)” checked:
$ sudo netstat -an | grep 590
tcp4 0 0 127.0.0.1.5902 *.* LISTEN
Which means that, in order to use it, you’ll have to first SSH in, and be using SSH to establish a tunnel through to the localhost port 5902 (i.e. heightened security).
SSH itself requires normal username/password.
You can turn SSH on via preferences -> sharing -> checkbox remote login”
If you want “global external” access in taht configuration then you’d need to somehow expose your boxes port 22 to the world through your router port forwarding. (according to the vine server docs).