With encryption support using SASL, client's won't be able to authenticate using PLAIN mechanism when encryption is enabled on the cluster. Today WebServer which is embedded inside Drillbit creates a DrillClient instance for each WebClient session. And the WebUser is authenticated as part of authentication between DrillClient instance and Drillbit using PLAIN mechanism. But with encryption enabled this will fail since encryption doesn't support authentication using PLAN mechanism, hence no WebClient can connect to a Drillbit. There are below issues as well with this approach:
1) Since DrillClient is used per WebUser session this is expensive as it has heavyweight RPC layer for DrillClient and all it's dependencies.
2) If the Foreman for a WebUser is also selected to be a different node then there will be extra hop of transferring data back to WebClient.
To resolve all the above issue it would be better to authenticate the WebUser locally using the Drillbit on which WebServer is running without creating DrillClient instance. We can use the local PAMAuthenticator to authenticate the user. After authentication is successful the local Drillbit can also serve as the Foreman for all the queries submitted by WebUser. This can be achieved by submitting the query to the local Drillbit Foreman work queue. This will also remove the requirement to encrypt the channel opened between WebServer (DrillClient) and selected Drillbit since with this approach there won't be any physical channel opened between them.