public void Configure(IApplicationBuilder app)
{
  app.UseStaticFiles();
  app.UseCookiePolicy();
  app.UseAuthentication();

  app.Use(async (ctxt, next) =>
  {
    if(ctxt.User == null)
    {
      // Not logged in, so nothing to do.
      await next();
    }
    else
    {
      // Set a scoped value in the NLog context, then call the next
      // middleware.
      var userName = ctxt.User.Identity.Name;
      using (MappedDiagnosticsLogicalContext.SetScoped("userName", userName))
      {
        await next();
      }
    }
  });

  app.UseMvc(routes =>
  {
    routes.MapRoute(
              name: "default",
              template: "{controller=Home}/{action=Index}/{id?}");
  });
}