[squid-users] Squid Session Helper

Hi,

I use the following setup:

User1
User2 => VPN (Server1) => Squid (Server2) => Internet
User3

And on the squid I use the session helper with these settings:

external_acl_type session concurrency=100 ttl=3 %SRC
/opt/squid32012/libexec/ext_session_acl -a -T 3600 -b /tmp/

The active session works and redirects to the license agreement and
saves the state for 1 hour. But because of the VPN on Server1 all the
user have the same source address, the address of server1. If user1
clicks ok, user2 will not see any redirect.

How can I make every user click the license agreement?

Thank you

Oliver