Cookies authentication in asp.net core 3.0 no working

Then i get User.Identity.IsAuthentication alway is false throught i login before with cookies authentication follow this artice.

When running the demo project from here,
https://codeload.github.com/aspnet/AspNetCore.Docs/zip/master

it also didn’t work.
I am using vs2019 tool
Is this a problem of asp core 3.0 preview?
Has anyone encountered a similar situation like me?

Many thanks,
Son Ho

.NET Foundation Website | Blog | Projects | Code of Conduct