Wow, David, thats a cool way.
But here another way:
Using NCSA Auth login
If you are using ncsa auth, create the user & password authentication list (you don't require users to be valid sme users)
touch /etc/proxyusers
Enter user names & password combinations one by one using this command
htpasswd -b /etc/proxyusers username password
You can test the authentication list using the following command
/usr/lib/squid/ncsa_auth /etc/proxyusers
Then enter the username & password when asked
You will see a ERR or OK response