Symptoms

The designer of a workflow is unable to see all the users that should be available from AD in their workflow. They cannot properly test or demonstrate their workflow's functionality without the full user list being properly populated.
 

Diagnoses

Captured a fiddler trace while doing the Synchronize Groups from the K2 for SharePoint App.
Frame ID = _2: failed at AjaxCall.ashx
....
 

Resolution

In order to get the Synchronize Groups service to work via the K2 for SharePoint 2013 app, we changed the SharePoint Integration service’s authentication type to use Service Account (SmartObjects Server Tester > SharePoint 2013 Integration > SharePoint Integration > edit the service instance and change the authentication type to Service Account). We were able to bypass the Login failed for user ‘NT AuthorityAnonymous Logon’. We also added the K2 service account to the Site collection administrator (MY URL).