LDAP, known in Microsoft circles as "OpenDirectoryŽ," is a protocol that is widely used to allow for
centralized control and management of systems. For instance, it makes it easy to use "single sign-on," whereby a single user-id and password (or, access token or what-have-you ...) can be used on multiple systems and types of systems. Linux supports this in part through the
PAM = Pluggable Authentication Modules facility, which allows it to consult LDAP instead of using its own facilities.
LDAP is, quite frankly, an arcane system ... and yet, it is a standard. There are many, many online tutorials and books on the subject, and you should begin with some that are overviews of what LDAP can do. Such as, say,
this one. You will find that it is
very important to understand the peculiar concepts and buzzwords of LDAP.
While you are learning about this general subject, you should also familiarize yourself somewhat with
Kerberos, which is an encryption-based scheme that assumes an unsecure network. It fulfills more-or-less the same role but does it in an altogether different way. You are most likely to find one or the other being used.
