Impersonation with .Net Core for web app

I'm attempting to create middleware using this post as a guide: https://aleksandarsimic.wordpress.com/2016/07/21/asp-net-core-1-0-iis-impersonation/ for a .Net Core Web Application.  

When I paste in the code I get several errors, but the most troubling is that there doesn't seem to exist a WindowsImpersonationContext in System.Security.Principal.   

I'm just hoping someone can confirm that Impersonation is not yet part of .Net Core.  I'm on .Net Core 1.1.0, using System.Security.Principal 4.3.0