OpenID Connect support
Uffd only implements OAuth2 with a Userinfo Endpoint, not OpenID Connect (OIDC). The OIDC Core specification adds a JWT id_token field to the Token Endpoint response and standardizes claim names (user attributes returned by the Userinfo Endpoint and baked into the id_token). OIDC extentions add IdP discovery and RP registration mechanisms. There are also drafts for front-channel and back-channel logout (single logout).
I originally decided against implementing full OIDC support, because it was not supported/required by any of our SSO-connected services. It seems like this might slowly change. At least we had a few situations where OIDC support would have simplified things. What remains is that OIDC (as a protocol) is much more complex and the JWT stuff does not provide any advantage to us (it only really makes sense in federated setups). The (IMHO) most interesting part would be back-channel logout, but I'm not aware that any of our services implement it (it is also still a draft).
Technically our OAuth2 library claims to support OIDC and the migration guide looks easy enough. In addition to the core spec, I think OIDC Discovery support would be necessary for OIDC support to make sense.