Umapathy, thank you for the answer.
I have Druid data source which REST API operates with POST methods that include JSON message body (http://druid.io/docs/latest/querying/querying.html).
As I understand, the only way is to add Middleware layer to work with the Druid api. So the way will be like this:
Druid -> Middleware layer (REST which allow to work with GET methods) -> Syncfusion dashboard (web data source).
Please correct me if I am wrong
Thanks.