chrisc297 on a quick test:
- Login with Twitter (OAuth1.0a) works as expected
- Login with Twitter (OAuth2.0) causes errors.
I know fof/oauth is setup for Twitter OAuth1.0a only (although I'm not certain why we don't use 2.0 at the moment, everything is in place to support it with just a few modifications). When you created your app at Twitter, did you check Request email from users? Also, the Client ID and Client Secret - ensure these are OAuth 1.0a keys, not OAuth 2.0