Earlier quoted context omitted.
https://identityserver.io/ https://fusionauth.io/ https://www.keycloak.org/ https://www.gluu.org/ Basically all of them can run in a container, it's just hosting a few endpoints and generating tokens. The complexity is in the protocols and not the app. Some of them offer a user database as well and might require a SQL DB connection.
The difference is probably between "can be made to run in a container" (which is true for almost every app) and "designed from day 1 to be containerized" - which is obviously not true for solutions like Keycloak. That being said, I'm not quite sure to which feature OP was referring in particular. Perhaps to the modular approach taken by Hydra when compared to Keycloak. Hydra has a much smaller scope than Keycloak, so…
Re: Show HN: Hydra – Open-Source OAuth2 Server
#51Ugh, I run Keycloak in a cluster of containers. Didn't have a bespoke solution, used Redhat's solution.