title: Get `ICredentials` from Windows Authentication
body: <p>I'm using Windows Authentication.</p>
  
  <p>I need to log into a service. It requires authentication using an <code>ICredentials</code> object, but would rather avoid asking for the user to enter their credentials again.</p>
  
  <p>Is there a way to get the <code>ICredentials</code> from the currently logged in user?</p>
  
  <p>The service is the TFS SDK.</p>