rpcInvoke = function(app, sid, namespace, service, method, args, cb) {
  app.rpcInvoke(sid, {namespace: namespace, service: service, method: method, args: args}, cb);
}
Push all the customized changes to the frontend internal session.

@param  {String}   frontendId cooperating frontend server id
@param  {Number}   sid        session id
@param  {Object}   settings   key/values in session that should be push
@param  {Function} cb         callback function

@memberOf BackendSessionService
@api private