LDAP Authentication on AD LDS

Hi,

I would like to publish an extranet website. We placed this website in a DMZ behind TMG and store the customers contact on an ad lds instance in order to avoid having non-corporate identity in our ad ds.

Extranet <--> TMG <--> Internet
                        |          
          ADLDS --|

We are hardly trying to configure TMG to let the customers authenticating on the AD LDS but facing issue. Following the dd440987 article, this should be OK.

However, I'm in trouble to fill the Domain field since AD LDS doesn't have one...

Am I wrong somewhere ? Is there anything I missed up ?

Thanks in advance for any feedback !