etag property

etag is used for concurrency control.

An etag is returned in the response to GetAcl and CreateAcl. Callers are required to put that etag in the request to UpdateAcl to ensure that their change will be applied to the same version of the acl that exists in the Kafka Cluster. A terminal 'T' character in the etag indicates that the AclEntries were truncated; more entries for the Acl exist on the Kafka Cluster, but can't be returned in the Acl due to repeated field limits.

Optional.