Experimented with Chrome extension OAuth using Chromium developer's library. Minimal success.
Added oauth2 chrome extension library and made small modifications to get it to work. Performs the authorize dance and invokes its callback, although actually using an example Google API such as the Tasks API has not been shown to work yet.
Created a Dwolla adapter for the oauth2-extensions library and used it to successfully reach the authorize callback. However, it seems that maybe the Dwolla Offsite APIs were the right choice after all. Will investigate.