To my knowledge, there is no way to "map"
the accounts (I could be wrong).
Though I did this same move (To LDAP) a few years back and I'll tell you
what I did:
Setup the LDAP, get that working for your admin user. Then add
Extension:RenameUser [1] . Then rename all your users from their old
account names, to what it will be in LDAP (before they get to login). If
you've got a lot of users, this will suck, but you only have to do it once.
-Jon
[1]
http://www.mediawiki.org/wiki/Extension:Renameuser
I suppose you could add another LDAP property containing the wiki name
and use that as username.