Heh -- I wish! http://psa.matiasaguirre.net/docs/pipeline.html is the best I found, though I tried to supplement it with additional docs here. On the plus side, I found the python-social-auth code to be of very high quality, so reading it was often easier than reading docs.

The pipeline design turns out to be pretty straightforward once you understand it, but getting that understanding is a bit tricky. I'm happy to sit down and do a brain dump over VC if that would be helpful.