Pinging @elastic/es-security (Team:Security)

Not sure I understand the difference between the timeout applied on the MasterNodeRequest vs. the submitTask.

The timeout on the MasterNodeRequest applies to routing the request from the coordinating node to the master (i.e. it's how long it waits to discover a new master if the old master fails) whereas the one on the submitTask call determines how long the task will sit in the elected master's pending task queue waiting for other tasks to finish processing before it gives up and fails. That said, in almost every other API we pass the ?master_timeout request parameter to both of these places, so the behaviour of these APIs is inconsistent.

Should we be passing in request.masterNodeTimeout() to the MasterServiceTaskQueue#submitTask in the following:

Yes. Probably. The trouble is that today once these tasks make it to the elected master they will today sit in the queue for as long as it takes to execute them. That's likely an oversight, but it's one which dates back a very long way. Changing this to align with the common ?master_timeout behaviour in most other APIs would drop this timeout to 30s and that might cause some visible breakage in cases where the master is busy doing other tasks.

Also, I am correct to assume that the ackTimeout (w.r.t. cluster state updates) only applies for AckedClusterStateUpdateTask and AckedBatchedClusterStateUpdateTask tasks ?

Technically it applies to all tasks that implement ClusterStateAckListener and to all task executors that supply an ack listener on success via ClusterStateTaskExecutor.TaskContext#success(Runnable, ClusterStateAckListener)), but mostly that's AckedClusterStateUpdateTask and AckedBatchedClusterStateUpdateTask indeed.

I think PostStartBasicRequest could be a MasterNodeRequest

Possibly, but possibly also the tasks which adjust the license should be made into acked tasks? It'd make sense to me to have these tasks wait for the updated license to be applied on all nodes, rather than just on the master as happens today.