Meta server: reset connection instead of returning permission denied when delegation token is no longer valid, in order to simplify the client library handling, and avoid possible ambiguity, the client re-connection logic should be sufficient to properly handle this case.
Chunk server: enforce delegation token lifetime by resetting connection in the case when the toke expires and a new rpc arrives. With connection pooling / and re-use this might potentially cause a problem with communications between chunk servers, though with reasonably long (several hours) delegation tokens lifetimes such spurious connection resets should not make much difference.
Chunk server: implement "opportunistic" remote state machine re-connect in the case when never valid more recent credentials available, the current session is about to expire, and no RPCs are presently in-flight.