Add counter to the key

[shawnlocal]

Hi
Thank you so much for this amazing project. I used to tunnel JF to my vps and add oauth on top of that but I started using this and i am in love with it.
It would be great to add counter to the keys. When we want to create the keys we would be able to specify how many times the link can whitelist IPs. Like if we set to 3 users can only use the link 3 times and after 3 times it deactivate the key.

Again thank you so much