Nabu Casa - securing the connection

Edit: I have reworded this post as I feel it is an important topic which deserves some attention.

1 How does one lock down Nabu Casa usage?
2 How do I know if my system is being access by another person through Nabu Casa?
3 How do I refresh the Nabu Casa keys so any unwanted connections can be eliminated ?

With a VPN tunnel I can test the IP it issues to know when the tunnel is in use and get a notification.
Also with a VPN I can also restrict the number of IPs that can be issued.

Thank you for your help.