Disable autologin on unknown clients

To enable autologin on clients, we use the following in lts.conf:

[Default]
LDM_AUTOLOGIN=True
LDM_PASSWORD=xxx

[mac01]
HOSTNAME=pc01

[mac02]
HOSTNAME=pc02

We put LDM_AUTOLOGIN and LDM_PASSWORD globally under [Default] to make lts.conf smaller. Sometimes HOSTNAMEs come from DNS so we don't have any [mac] sections in lts.conf at all.

The problem is that unknown clients try to login with an account of ltsp123/xxx, which doesn't exist, so they end up on an endless failed autologin loop with no error messages, which seem like failed Xorg restarts to the users.

Please either provide a method to disable autologin on unknown clients, or to stop autologins if it failed the first time.