title: How to get the current logged in user ID in ASP.NET Core?
body: <p>I've done this before with MVC5 using <code>User.Identity.GetUserId()</code> but that doesn't seem to work here.
  The <code>User.Identity</code> doesn't have the <code>GetUserId()</code> method.</p>
  <p>I am using <code>Microsoft.AspNet.Identity</code>.</p>