When working with authentication protocols the commonly used technique in the past was known as authentication by assertion. In this scheme a user logs in to their machine which then authenticates their request to a remote server. Once the authentication is finished the user can then communicate with other services. This provides a very low level of security, which has led to numerous vulnerabilities in the early versions of the rlogin Unix login utility.

An alternative solution is for the user to repeatedly provide their password each time they wish to use a service. This however requires the user to send their plain text password over the network, which could potentially be intercepted by a third-party user and can get …