There are few breaking changes in Asp.Net Core Identity in net core 2.0. One of the major change is removing navigation properties from Identity entities like IdentityUser, IdentityRole.
This project Obsolete now. For sample with new builds of Identity Server 4 check official sample repo of Identity Server.
I build simple Auth server sample using Identity Server 4 and ASP.Net Identity membership service. You can fork the repo and customize it as per your need. This is just a basic sample but i am working to add other advance pieces too.
Project is on Github.
Happy Coding 🙂