that a sniffer trace of the traffic going to the server.
Then check the server response for a line which looks like : set-cookie: name=value.
This means the server will always use the cookie "name" and a different "Value" for each client.
So you configure ACE to look for hte "name" and it will learn the "value" automatically.
If you really do not understand http cookies, you could simply use the "sticky cookie insert" feature.
ACE will do everything for you automatically.