1. client authentication cert: needed for the portal to resolve the web reference of WCF service, to send request to the web service server, to setup SSL channel.
2. server authentication cert: needed for the portal to setup SSL channel (encryption) with the web service server.
Note, server authentication cert is not used for client authentication. In other words, in the web service's web.config,
Note: both client auth cert and server auth cert are required for SSL channel setup.