So I'm doing a bit of an experiment, the idea being that if you have a group of tor users sharing common infrastructure then its a slightly different situation then one lone user, and you wantto emphasize that resources should not be shared, caching should be minimal and non-persistent, you need to keep usage from standing out, etc. The problem with my original idea is that everything that does HTTP <> SOCKS is one or two decades old, and draws a lot of attention because it forks for every connection or is some strange process that nobody has ever seen before.

So plan B is everyone involved runs their socks speaking browser on their desktop/laptop, everyone runs a tor client on the same device as their browser, we use the HTTPProxy/HTTPSProxy feature of the clients to navigate the firewall, everyone uses their own credentials instead of having one ID draw attention for high utilization, and the presence of the Proxy-Authorization header takes care of any caching/session sharing issues along the way. 

To make that work, the one question I have for tor-dev is if its possible Here:

https://github.com/torproject/tor/blob/24f170a11f59e26dec3a24d076b749c8acc793ca/src/or/connection.c#L1865

To work back to the socks_req, so that I can pass through the username and password to the upstream proxy instead of the one global username/password?