i just upgraded from 4.0.12 to 4.2.0 and my backup job failed last night.  I spent a few hours troubleshooting the issue and it appears mongodump can no longer backup data directly on a secondary like it used to.  If fails to allow listDatabases because it doesnt set rs.slaveOk() first.  For my use case, i have 4 replicas, 3 of which are used by our API and the 4th is hidden just to use for backing up and maybe the occasional long query.  I see that i can specify a read preference, but i need to ensure no impact to the non hidden members which are being queried constantly.  Can we have a parameter to set slaveOk?  I have temporarily downgraded just the hidden replica to 4.0.12 so backups can continue.