Enable Windows Authentication:
How to make Windows Authentication prompt a user when opening the ARS WI?:
Remove Kerberos Provider and use NTLM. The default logon type with Windows Authentication is Kerberos (users token). But if it can't get a token it fails to NTLM, where the user is prompted to authenticate.
Note: If the URL is not in either the Trusted or Intranet zone, Kerberos Authentication will not be used, as IE will only hand over the ticket to one of those two zone (Internet and Untrusted are never sent a token). However Firefox and Chrome would also need the ARS websites URL included in their config settings, as they tend to ignore Windows "Internet Option" and the zone settings.