I'm currently performing an exercise to lock-down ESXi servers against the 5.5 Hardening Guide.
One of the actions (enable-auth-proxy) requires the setting-up of an Authentication Proxy service (which may or may not be the same server that is running the VCenter service).
Some of the documentation I've see suggests that AutoDeploy is needed as a prerequisite to installing Authentication Proxy, ie:
vSphere 5.5 Documentation Center
Could somebody clarify please as I don't currently have Autodeploy configured and have no intention of doing so at this stage.