title: Resolving TFS WorkItem Assigned-To and Created-By to email address
body: <p>I'm working with some custom reporting in TFS. I have a set of <code>WorkItem</code> instances that I want to get the information about the Creator and Assigned-To from.</p>
  
  <pre><code>WorkItem wi = GetWorkItem( ... );
  String assignedTo = (String)wi.Fields[CoreField.AssignedTo].Value;
  String createdBy  = (String)wi.Fields[CoreField.CreatedBy].Value;
  </code></pre>
  
  <p>The problem is that the fields are raw string values that contain the display-name of the user. I have to store my own database that maps these display-names to their Active Directory identities (by their username or email address).</p>
  
  <p>Obviously maintaining my own parallel database of users isn't the right way - is there any other way to get from <code>wi.Fields[CoreField.AssignedTo].Value</code> to a security identity object, or at least the user's username or email address?</p>