Retrieve custom params from doSync in Rhoconnect server

As explained in the linked documentation, custom parameters can be passed to RhoConnect server using:

Rho::RhoConnectClient.doSync(false, "param1=abc")

However, the documentation does not explain how to fetch and use these parameters in RhoConnect server. How can I retrieve param1 in the model's query method?

docs.tau-technologies.com/en/5.5/guide/using_rhoconnect#controlling-synchronization-programmatically