I would guess that it should look somewhat like this:
auth "localhost" {
hosts: "localhost, 127.0.0.1, stdin"
default: ""
}

access "localhost" {
users: ""
newsgroups: "*"
}
auth "localnet" {
hosts: "192.168.0.0/24"
default: ""
}

access "localnet" {
users: ""
newsgroups: "*"
}