Hydra feels mature. I think it's their longest-developed product so far. Besides breaking changes during big upgrades(v0 -> v1beta -> v1), everything has been painless:
- It runs anywhere with or without containers
- API makes sense, good SDKs are available in all my used languages
- RAM usage is surprisingly low compared to usage and has been great for resource-constrained environments
- Stateless means horizontal scaling is as easy as `replicas++`
- Sub-millisecond response times for some calls, much faster than our previous setup
With Hydra, I know it's the client's fault when OAuth calls fail and not just a buggy server implementation. This is reinforced in dev mode with great errors like:
- The authorization code has already been used
- The request is missing the response_type parameter
- Parameter "nonce" must be set when using the implicit flow
On the flipside, Oathkeeper is not a mature product and has not yet reached v1. There are breaking changes planned [1]. It lacks support for at least one popular usecase (mine) out of the box [2]. Rules can be hard to create and debug. I wouldn't recommend Oathkeeper in its current state unless you're ready to dive in and fix things yourself. Once configured it sticks with the Ory trend: fast, lean, and stable.
Depending on your usecase, Oathkeeper could be swapped out with any IAP like Pomerium or just with your reverse proxy's auth request support + some small custom shim.
I haven't tried Keto (access control) or Kratos (user management) yet. Kratos is on my todo list.
We are using Ory Hydra now (but not any of the other components like Kratos, Oathkeeper, etc) and no real complaints so far. It is important to understand though the Hydra is just a component and not an out-of-the-box solution. You still have to implement your own user interface is you plan on doing OIDC login (and not just client_credentials for service authentication). Basically Hydra just takes a self-hosted login/registration/etc UI which you build yourself and wraps it in an OIDC provider. Which is great if you need to build an OIDC provider and want tight control over the user experience and user management (our use case) but don't want to implement all the fussy details of the OAuth2 protocol.
