Windows Authentication: fail to get User.Identity.Name in controller (always null)

[wenkangjing]

Project was generated by yo aspnetcore-spa - React With Redux, with following settings

launchSettings.json

    "windowsAuthentication": true,
    "anonymousAuthentication": true,

Symptom
User.Identity.Name; is always null in any controllers

Walk around
Set anonymousAuthentication to false can walk around it, but just curious why.

[SteveSandersonMS]

Would you mind posting this at https://github.com/aspnet/Identity/issues, since it's a general question about identity in ASP.NET Core rather than being specific to the SPA templates? Thanks!