A CoA request is a network protocol message used in the context of network access control and authentication systems. It is typically employed in scenarios where a user's access privileges or attributes need to be modified during an active network session. CoA requests are commonly used in conjunction with the RADIUS protocol, which is widely used for managing user authentication and authorization in network environments. When a CoA request is initiated, it is sent by a network access server (NAS) to a RADIUS server to request a change in the user's authorization state or attributes. The CoA request contains information specifying the desired change, such as granting additional access privileges, revoking existing privileges, modifying session parameters, or updating user attributes. The RADIUS server processes the CoA request and applies the necessary changes to the user's session in real-time, allowing dynamic adjustments to the user's authorization and network access. CoA requests are often utilized in scenarios where an administrator needs to promptly update a user's access rights without requiring them to terminate their current session. This flexibility is particularly valuable in environments that demand fine-grained access control or where access privileges need to be adjusted based on changing circumstances or policies. References := Some possible references for this answer are:
* RADIUS Change of Authorization - Cisco
* What is a CoA Request? - Portnox
* RADIUS Change of Authorization: Explained - Cloud RADIUS