I have a Zentyal 8 installed as a primary domain controller. I installed its squid module to permit users from my LAN network Internet access. I'd like they use their domain credentials. How can I do that?

I can see squid.conf.mas file with some ldap authentication code. So I suppose there is an easy way using web interface. But there is no authentication options there. I even tried to put some ldap authentication code inside that file but, with some code already there it is a shame to that.

By default Zentyal's squid module allow Internet access without asking for user's credentials.

I would appreciate any help.