TACACS+ is not a Cisco proprietary protocol. It was developed by Cisco as an extension to TACACS, but they did so openly, submitting a draft RFC and releasing a development kit to allow others to adopt the protocol. There is a more current IETF draft under way as well - https://datatracker.ietf.org/doc/draft-ietf-opsawg-tacacs/ TACACS+ can be used for Authentication, Authorization, and Accounting - a common use case is for command-level authorization on Cisco devices, but that's due more to how long Cisco has been implementing and pushing the standard rather than because that's all it's good for. In many customer environments, it is replacing or has replaced RADIUS as the AAA standard. In the case of a Palo Alto Networks firewall or Panorama, we can leverage TACACS+ to authenticate a user, as well as authorize the user to perform specific functions though the use of a role, all without needing to define each individual user in Panorama or on the firewall. This is exactly the same use case as RADIUS, it's just another (and much more secure) option for doing so.
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