I didn't have permission to modify r/8437/, so I'm posting this as a separate RR. A decent portion of this diff is stuff that Dominic did. Anything involving social authentication is stuff I did.
Users may now authenticate with GitHub, associating their RR account with their GitHub account. When a webhook pull request is incoming, it will attempt to find a user with that GitHub username and submit it under their name, else it submits it under a dummy account (No_Submitter).
I have also added the ability to authenticate with a BitBucket account. The data is currently not showing up in the database even though it successfully authenticates.

Nothing except testing that it actually works - no unit tests or attempting to break it.