The SmartLdapGroupStore is designed to discover information about groups of users defined within an LDAP directory server. It queries an LDAP data source for a collection of group objects and uses their attributes to organize them into a hierarchy. It uses Person Attributes to determine which users belong to these groups.

Although there are existing implementations of GaP that can leverage information from LDAP in some fashion - PAGS, LDAPGroupStore, JitLDAPGroupStore - none of them can do what SmartLdapGroupStore does: discover groups. They all rely on local configuration where they groups they support must be defined explicitly.

See wiki page: http://www.ja-sig.org/wiki/display/UPC/SmartLdapGroupStore