I don't know oauth at all, but that was the area that always felt convoluted when i'd research it. I think i'd be much happier if they had sub spec names with very specific use cases. OAuth2 Client Redirect, OAuth2 Server Authority, or w/e.. i'm just making stuff up for attempted clarity.
Then I want an easy story for linking that instead to LDAP for corporate deployments, or to an SSO OAuth server.
The problem is...well I still don't really know how I should be including that? It's so much easier just to register a session cookie from a login page.
For a webpage this makes perfect sense, where would you securely store an access / refresh token on web that isn't vulnerable to XSS? In a session cookie that is secure & http only...
For native apps though that state might be more annoying to track and a auth token and refresh token is pretty easy to store securely.