Authenticating user against Windows cache when Active Directory is not available

My application needs to authenticate a user against active directory and determine the list of groups the user is a member of. I've developed a VB6 app to do this and it works fine.

The customer has come back and said they need the app to authenticate users even if active directory is not available (machine off network), similar to how Windows will still allow a user to log on to a system if a machine is off the network, if they've logged onto the machine previously.

How do I go about accessing 开发者_如何学JAVAthe cached user information in VB6? I'm currently user ADI and LDAP.