I just found the answer to this question in the Crestron Labs forum under Cisco room devices driver 3.2.4 beta release. Then I realised I was looking at the API for SX80 which hasn't been update since 2017.
I was then able to find the information in "Cisco Collaboration Endpoint Software API Reference Guide CE9.10" -
xCommand Conference Call AuthenticationResponse.
Applies to: All products
Requires user role: ADMIN, USER
This command is only available for Cisco Webex registered devices. The command gives a
response to an authentication request based on the Conference Call[n] AuthenticationRequest
status.
USAGE:
xCommand Conference Call AuthenticationResponse [CallId: CallId]
ParticipantRole: ParticipantRole [Pin: Pin]
where
CallId:
Integer (1..65534)
Unique identifier of the call. During a call you can run the xStatus Call command to see the
CallId.
Default value: 0
ParticipantRole:
Host/Panelist/Guest
Host: Join as host.
Panelist: Join as panelist.
Guest: Join as guest.
Pin:
String(0, 32)
PIN code. Must be provided if joining as host, panelist or as guest when the Conference
Call[n] AuthenticationRequest status indicates that a PIN code must provided.
Default value: ""