Selects whether and how aggressively SSG's Auto-Domain feature runs, which automatically maps a subscriber to a service based on their APN or a structured/realm-qualified username, without the subscriber picking a service manually. The choice of basic vs extended determines how much of the username/APN parsing logic SSG applies before falling back to manual selection or the default network, so choosing the wrong mode for a given username scheme causes subscribers to land in the wrong service, or none at all. A mobile operator whose GGSN hands SSG usernames like 'alice@corporate.apn' would set cssgCfgAutoDomainMode to extended(3) so the 'corporate.apn' realm auto-selects the corporate VPN service instead of leaving the subscriber unauthenticated.