Omniauth is for implementing an OAuth client, and it's great... but, that's the other side of this coin.
There are very few good provider libraries out there, making it harder to stick to standards. People who want to provide an API shouldn't have to re-invent the wheel every time.
I like doorkeeper as well. Opro doesn't currently support any other backends other than ActiveRecord, so if you're using mongo you would need to use doorkeeper.
I started writing opro before DK was out in the wild. There were some things I had in opro that weren't in DK so I decided to keep developing it.
Last time I checked here are some differences:
- Deals with CSRF protected resources automatically
- Works with your login system (like devise), not around it. No special casing or configuration is needed
<3 doorkeeper. Using it to make one of our open source apps - http://github.com/isotope11/xrono - an oauth provider to support an oauth sso flow inside of apps we've built for internal use regularly. It took an hour one night to build the provider, and maybe an hour to build the omniauth provider gem and integrate it into an app.
P.S. - it also took like six hours of banging my head against a wall for unrelated oauth-related problems, but not DK's fault.
There are very few good provider libraries out there, making it harder to stick to standards. People who want to provide an API shouldn't have to re-invent the wheel every time.