LDAP is rapidly becoming a de facto standard for remote authentication and authorization of users, not only in the realm of Linux, but also in that of Windows where it is a key component of Active Directory. Usage of LDAP is also becoming increasingly widespread in wireless networking systems. For example in hot spots, ISPs will sacrifice data security for the sake of convenience by not using encryption, but will use LDAP to restrict access to the Internet to people who have purchased pre-paid access codes with a predefined lifetime.
Chapter 32, "Controlling Web Access with Squid," covers the use of the Linux Squid application to cache Web content, restrict Web access by the time of day and via password prompts. Although it is beyond the scope of this book, you should know that you can use LDAP to complement the functionality of Squid in larger implementations.