This is a "how to" on setting proxy on you Raspberry PI when
1) The proxy uses a PAC file and is something like http://school-proxy.com:8080/proxy.pac
2) Requires you to authenticate with a username and password
Now, I followed this : viewtopic.php?f=28&t=18634
but it only works when you don't have a pac file. I did and this didn't work.
So, I did some learning and found the purpose of a PAC file. In layman terms, its a lookup list that has your company's or your school's or your institution's proxy servers mentioned. Let's say your environment has 10 subnet and each subnet has it's own proxy server. Then the pac file will be used by your client machine to lookup the proxy server assigned to a specific subnet.
So, I fetched my PAC file, by typing the exact proxy URL in my browser. Something like : http://school-proxy.com:8080/proxy.pac
This downloaded the PAC file and I was easily able to find the proxy server assigned for my IP / subnet.
One I had that, it was pretty simple.
I used this really nice tool called pi-proxy which can be downlaoded from https://pi-proxy.net/
I typed in the exact proxy server's hostname that was assigned to my IP / subnet.
Specified the port.
Put in my credentials, enabled it, and rebooted the pi once asked to.
And walla, Bob's your uncle !!!