Recently I was working on a project where I have to build simple Authentication Server. For that project, i need to use Resource Owner Password (ROP) OAuth flow with persistence storage of all data. Also, need to handle Social Signup/login with ROP flow. Facebook and Google as third party Identity Provider is available in this sample ( up to now)
So I am using Identity Server 4 and Entity Framework core to build this simple authentication server. This sample might be helpful if you are working on same as my requirement.
Also, I am extending this sample to support other OAuth flow in future.
Here is project link in Github.