I've recently tried out Keycloak(https://www.keycloak.org/) and have been impressed with it. Saved at least a few weeks on a personal project. It does have a learning curve though.
I've been tasked with implementing oauth/openid at work and in about one month in spare time i was able to read rfc 6749, install keycloak, configure it, create a client, create a very basic app (~80 lines of python and flask) and log in via oauth/openid with user information and groups pulled via LDAP.
I've been usjng keycloak as an UMA authorization server, and while it's better than nothing it has a few bugs that make it not exactly compliant with the spec. Additionally the UI is incredibly confusing and the documentation isn't that helpful in some cases. Anything you want to do you have to spend too much time searching the UI and some things are not even available: Want to assign ownership of a resource to a user? Need to run a curl request.
Though I haven't tried other implementations, so maybe this one's the best
