Also, you can use the approach from the following KB to access the XHR object: https://www.telerik.com/support/kb/aspnet-ajax/client-data-source/details/add-authentication-request-headers-with-clientdatasource

Parameters can vary wildly in their format depending on the service that is to be consumed. Thus, a simple property would be unable to satisfy most scenarios.
At the moment, there are two built-in options to provide parameters to a data source:
- add a filter expression: https://demos.telerik.com/aspnet-ajax/clientdatasource/functionality/filtering/defaultcs.aspx
- use the OnCustomParameter event to set the desired arguments: https://docs.telerik.com/devtools/aspnet-ajax/controls/clientdatasource/client-side-programming/events/oncustomparameter

For more flexibility, I recommend you use the Kendo DataSource widget that allows you to pass parameters to its read configuration or to even invoke your own function: https://docs.telerik.com/kendo-ui/api/javascript/data/datasource/configuration/transport.read
As a general rule of thumb, for client-side binding scenarios I recommend you use the Kendo widgets over the UI for ASP.NET AJAX controls, because the Kendo widgets are designed to work on the client, while the WebForms controls are, first and foremost, server controls with server rendering and data binding.

You can also create your own requests (e.g., with jQuery) and consume the data in their callbacks.