Kerberos

Kerberos is designed to enable two parties to exchange private information across an otherwise open network. It works by assigning a unique key, called a ticket, to each user that logs on to the network. The ticket is then embedded in messages to identify the sender of the message.

Kerberos is a secure method for authenticating a request for a service in a computer network. For more information, please refer to this page
http://www.networksorcery.com/enp/protocol/kerberos.htm.