title: Get ClaimsPrincipal from usermanager
body: <p>In a ASP.NET Core Controller I can Access <code>User</code> to get all current user claims as <code>ClaimsPrincipal</code>. Now I added a new user using <code>userManager.CreateAsync</code>, added some claims and need all his claims as a ClaimsPrincipal for some other function.<br>
  I tried the following:</p>
  
  <pre><code>  var user1 = new IdentityUserEntity
    {
  // set username and stuff
    };
    var result = await userManager.CreateAsync(user1, passwort);
    await userManager.AddClaimAsync(user1, new System.Security.Claims.Claim(MyClaimTypes.Stuff, MyClaimValues.Whatever));
  </code></pre>
  
  <p>afterwards I created a ClaimsPrincipal like this:</p>
  
  <pre><code>  var user1cp = new ClaimsPrincipal(new ClaimsIdentity(await userManager.GetClaimsAsync(user1)));
  </code></pre>
  
  <p>Problem is, this ClaimsPrincipal does not contain the NameIdentifier (and maybe other stuff?).</p>
  
  <p>How do I get a complete ClaimsPrincipal from a user I freshy added to the database?</p>