Windows SQL Server Express 2012 and LDAP external server integration
Do you just want to configure this? Or are you not averse to writing some code?

In the latter case, it should be relatively easy to write a small program that connects to both the LDAP server and the database and synchronizes the data. I've written such a thing once in PL/SQL in Oracle -- if it's possible there it should be possible in most languages and environments!