Final answer:
Kerberos uses tickets to identify authenticated users, a feature not supported by RADIUS or Diameter. These protocols use shared secrets and attributes for authentication, lacking the ticket system that Kerberos employs.
Step-by-step explanation:
The feature that is supported by Kerberos but not by RADIUS and Diameter is the use of tickets to identify authenticated users. Kerberos, a network authentication protocol, is designed to provide strong authentication for client/server applications through the use of secret-key cryptography. A central part of the Kerberos protocol is the concept of 'tickets' which are used to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner.
RADIUS and Diameter are both protocols used for similar purposes but they do not use the concept of tickets. Instead, they rely on a shared secret and attributes that are passed between client and server for authentication and authorization. While RADIUS and Diameter support features such as services for authentication and single sign-on capability, they do not incorporate the use of tickets as Kerberos does.