.NET Core 3.1 User.Identity.Name always null with Windows Authentication

I am using Windows Authentication with a .net core 3.1 application. I would like to retrieve the current user name but it's always null. I have not been able to deploy this application to IIS yet so this is happening while debugging with IISExpress.

launchSettings.json:

{
  "iisSettings": {
    "windowsAuthentication": true,
    "anonymousAuthentication": false,    
    "iisExpress": {
      "applicationUrl": "http://localhost:52362",
      "sslPort": 0
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }
  }
}

Startup.cs:

public void ConfigureServices(IServiceCollection services)
        {
            services.AddAuthentication(IISDefaults.AuthenticationScheme);
            services.AddAuthorization();

            services.AddHttpContextAccessor();
            services.AddMvc();
            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
        }
        
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseAuthentication();
            app.UseRouting();
            app.UseAuthorization();
        }

Controller:

[Authorize]
[ApiController]
[Route("[controller]")]
public class FilingController : Controller
{
    private readonly string _currentUserName;
    public FilingController(IHttpContextAccessor accessor)
    {
        //This is always null
        _currentUserName = accessor.HttpContext.User.Identity.Name;
    }
}

Here is the Program.cs:

public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                    webBuilder.UseIISIntegration();
                    webBuilder.UseIIS();
                });
    }

This occurs after a successful login. Why is the Name null, how can this be fixed?