show connected users

[cad]

It would be nice to show currently connected VPN users and their location etc.

One way would be to talk OpenVPN's RPC protocol. The other would be arpsweep.

Notes:

• https://github.com/OpenVPN/openvpn/blob/master/doc/management-notes.txt

  # in server.conf
  management localhost 7505