Aha, I see. The only real difference between GitHub Enterprise and GitHub.com is a couple of URLs (github.com -> yourdomain, and api.github.com -> yourdomain/api/v3/), which is what I was hoping to be able to configure with my proposal :(

Judging by the code, it looks like the OAuth logic is fairly cleanly separated from the various specific OAuth implementations (which inherit from it). Instead of (or as well as) giving us a collection of hardcoded GitHub/Amazon/Asana/Disqus OAuth providers in the auth options, could there just be a catch-all configurable OAuth provider option?