How to distribute PAC file via GPO

Question

I'm new to the Sophos web appliance. We are migrating one of our divisions off of two VERY OLD proxy servers, IronPort and BlueCoat. We are moving to a Sophos web appliance. It is currently installed, basically configured and running, but not processing traffic yet. I need to GRADUALLY migrate users to the new appliance and want to use an AD GPO to control that process. I need some good, detailed information on where I should put the PAC file so that I can deliver the link via GPO and have it read and processed correctly by IE, Chrome and FireFox. 
 
 I also need to know where, in the GPO, the settings should reside. I've seen some older documents from 2012 that provide limited information, but I am looking for more current content that could assist me with this migration. 
 Thanks in advance for your time and input.

DarrenHarris · Answer

The easiest way i've recently found is to use wpad (web proxy auto discovery) using DNS (DHCP is also an option) 
 Basically you create an internal web server and create a wpad.[localdomain] dns CNAME entry pointing to it. Then create a wpad.dat file on the root (basically this is a pac file) 
 Then with automatically detect settings is ticked in internet options it picks up the config and applies it. 
 These links may should help 
 https://technet.microsoft.com/en-gb/library/cc995261.aspx 
 http://findproxyforurl.com/ 
 
 GPO wise you just have to look at enforcing the automatically detect settings option which is done by importing the registry setting, and if you want to lock it down you can disable the connections tab. 
 not sure on firefox, but for chrome you can import the chrome admx file and you can enforce chrome to use system settings, which uses the ie settings