Introducing IdentityManager2
IdentityManager is a project that was initially created and owned by Brock Allen who also created IdentityServer together with Dominick Baier. Scott Brady (https://www.scottbrady91.com/aspnet-identity) and his employer took over the project, ported it to ASP.NET Core, and released it as IdentityManager2 (https://brockallen.com/2018/07/09/identitymanager2/).
It is provided via NuGet (https://www.nuget.org/packages/identitymanager2).