David and Katherine Goodwin

I was going to suggest LDAP, but this will be really tricky if the machines are on separate networks. LDAP-integration is, IMO, most reliable when you have your LDAP server on the same subnet as the servers it serves. This is because LDAP integration also integrates UIDs, GIDs and so on, in addition to passwords for authentication. I suppose you *could* try using LDAP slaves on the remote networks, but that might take a bit of effort to get working.

Perhaps try LDAP on your local machines first, then try extending it?