We have a liferay application where users are first registered on an directory server and post approval are imported/created at liferay end.What considerations/scenarios need to be considered to take a pick between authenticating user with LDAP restful web service or by importing them and authenticating them by application in-house mechanism?
From my point of view you must to use an LDAP if you have to manage several groups or entities in a massive way or if you want to share your User repository with other applications (Think about LDAP as a Master User schema)
If you just need to Auth them through your portal and there is not any other scenario use the in-house mechanism that Liferay provides.