QuorumServer will do the authorization checks against configured authorized hosts. During LE, QuorumLearner will send an authentication packet to QuorumServer. Now, QuorumServer will check that the connecting QuorumLearner’s hostname exists in the authorized hosts. If not exists then connecting peer is not authorized to join this ensemble and the request will be rejected immediately.
In branch-3.4 building authzHosts list is pretty straight forward, can use the ensemble server details in zoo.cfg file. But with dynamic reconfig, it has to consider the dynamic add/remove/update servers and need to discuss the ways to handle dynamic cases.