Ask HN: The best place to start for open identity / access control mgmt?

What are the recommended libs and frameworks to use for an open identity and access control management system for web apps? We have existing apps / user-data dbs. There are new web apps to be built in short order. We're looking to unify authN and authZ facilities across them all. OpenID and OAuth seem the way to go; where to start for authentication and app-by-app access controls? Thank you.