Right now, during RPC Connection establishment, all SASL requests are considered as OutOfBand requests and handled within the same Reader thread.
SASL handling involves authentication with Kerberos and SecretManagers(for Token validation). During this time, Reader thread would be blocked, hence blocking all the incoming RPC requests on other established connections. Some secretManager impls require to communicate to external systems (ex: ZK) for verification.
SASL RPC handling in separate dedicated handlers, would enable Reader threads to read RPC requests from established connections without blocking.