Tracking open/close connections efficiently?

Hi!

(This is not an issue, sorry if it's not i the right place)

I'm wondering if there is a way to track when a user is connecting, but also when disconnecting, with guarantee about the disconnect (connection closed, lost, exception, error, etc).

The idea is to implement a counter to track the number of active connections at a specific time to limit the abusers.

Thanks in advance :)