title: ImmutableID of the user missing when trying to acquire a token for MS Graph API (Windows auth)
body: <p>I'm developing an API that uses the Microsoft Graph Client SDK to make multiples calls to a Sharepoint site.</p>
  <p>To authenticate the users making the calls to the API, I'm using the Integrated Windows Provider method, with this very simple code:</p>
  <pre><code>var clientApp = PublicClientApplicationBuilder
      .Create(_apiSettings.Value.AzureClientId)
      .WithTenantId(_apiSettings.Value.AzureTenantId)
      .Build();
  
  var token = clientApp.AcquireTokenByIntegratedWindowsAuth(new string[] { _apiSettings.Value.MicrosoftGraphApiScopeUrl })
      .ExecuteAsync().Result;
  </code></pre>
  <p>When calling the method containing this code in local, it works flawlessly. But when I deploy the app to our test server, and by using the NTLM authentication with the same user than in local, I'm having this error:</p>
  <blockquote>
  <p>Microsoft.Identity.Client.MsalUiRequiredException: AADSTS90020: The
  SAML 1.1 Assertion is missing ImmutableID of the user.</p>
  </blockquote>
  <p>When printing the content of the HttpContext.User, I see that the same user, connected to the same group, is both used on the &quot;online&quot; and the local version.</p>
  <p>I already tried adding this header, but it's not doing anything:</p>
  <pre><code>var immId = new Dictionary&lt;string, string&gt;();
  immId.Add(&quot;Prefer&quot;, &quot;IdType=\&quot;ImmutableId\&quot;&quot;);
  
  var token = clientApp.AcquireTokenByIntegratedWindowsAuth(new string[] { _apiSettings.Value.MicrosoftGraphApiScopeUrl })
      .WithExtraHttpHeaders(immId)
      .ExecuteAsync().Result;
  </code></pre>
  <p>What can I do ?</p>
  <p>Thanks!</p>