Cookies authentication in 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,

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

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