I agree that the learning curve is too steep with OAuth and OpenID and that supporting multiple scenarios could be part of the problem.

One specific problem I've faced is that it's very complicated to configure a development environment for unit and integration testing. I think there is huge demand for something that works well for Docker Compose and unit testing frameworks while still being a production grade solution.

I haven't evaluated everything out there but so far the best solution I've found is Keycloak. Unfortunately it takes 20 seconds to start on my computer and up until very recently I had to go through the configuration procedure each time you launched tests. I was fortunate enough to get a PR (https://github.com/jboss-dockerfiles/keycloak/pull/152) accepted which allowed me to load a working configuration file directly into the unaltered Docker container with some users and roles for testing purposes.

So if you have something that starts quickly, is easy to combine with Docker Compose and with unit testing frameworks, and could be used in a production scenario... Let me know. ;-)

Oh, and it also needs to be on-premise.