I have installed ASP.NET Core 2.1 but even though I have created a new ASP.NET Core Web Application using ASP.NET Core 2.1 with
ASP.NET Core 2.1
ASP.NET Core Web Application
Turns out ASP.NET Core Identity is now available as a prebuilt package called Microsoft.AspNetCore.Identity.UI.
ASP.NET Core Identity
Microsoft.AspNetCore.Identity.UI
You can read more about it here:
https://blogs.msdn.microsoft.com/webdev/2018/03/02/aspnetcore-2-1-identity-ui/