E-mail addresses, netIDs, LAN accounts, and bar codes are examples of identifiers. Identifiers were simple when each person had exactly one. Now identifiers apply beyond people to objects such as printers and applications and to groups of subjects. Typically a real-world subject will have several identifiers. Thus the relationships among a subject s identifiers and the policies associated with the assignment of identifiers become important issues.
Authentication is the process of verifying a legitimate use of an identifier.
The traditional approach of login and clear text password is far too insecure and inflexible for the variety of ways that clients need to authenticate to servers. LDAP-based tools, Kerberos, and X.509 are modern alternatives. There are substantial technical and political issues in the development and operation of a directory service. Applications must be reengineered to use the directory. Policy issues include ownership of data, feeds into and out of the directory, and setting permissions to read and write data.