Install with:

apt-get install squid

The external authentication program that authenticates your proxy users against LDAP is now available as a module in the Squid package.

(parts of) /etc/squid.conf

....
http_port proxy.intra.example.com:3128
....
auth_param basic program /usr/lib/squid/ldap_auth -b ou=People,dc=intra,dc=example,dc=com -h ldap.intra.example.com -f "(&(objectClass=posixAccount)(uid=%s))" 
auth_param basic realm Squid proxy-caching web server
auth_param basic children 30
auth_param basic credentialsttl 2 hours
....
acl SquidLdapUsers proxy_auth REQUIRED
# You may put the line above just before the line
"acl CONNECT method CONNECT" in the squid.conf file.
....
http_access allow SquidLdapUsers
# You might put the line above just below the line:
# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
....

You can check the authentication program by hand:

Just type on the prompt:

/usr/lib/squid/ldap_auth -b ou=People,dc=intra,dc=example,dc=com 192.168.1.12

Now input “username<SPACE>password<ENTER>” pairs. The authentication module will answer back with OK or ERR. End the session with Control-D.

Start the proxyserver

/etc/init.d/squid start