With LDAP you can only look up certain values inside the directory.
PPTP as well as L2TP use a Challange Response mechanism to authenticate users. LDAP does not offer this kind of authentication mechanism.
This is the main reason why ASL does not support LDAP authentication for PPTP and L2TP.
if the clear text passwiord would be stored in the directory, ASL could simulate the authentication mechanism. But as the LDAP lookup is done in clear text, this would be pretty insecure.
