I just rebuilt ruby-github-api by relaxing the dependency on oauth2. I pulled the test cases from github to check if anything happens. It built just fine. 6 tests failed, but none related to OAuth2 (seems some keywords/options mismatch).
I think we could fix this by relaxing the dep on oauth2 for now. There is an upstream report asking for supporting oauth2 2.x at https://github.com/piotrmurach/github/issues/386. Regards, Daniel