How to set up a report's dataSource

Hello, I have a report, with no link to dataSource.

I would like to call it through REST API service (REST URL).

How can I set up:

1. dataSource which should be used? In JasperServer I have more dataSources Defined, but don't know hot to set it up from our app, which call reports.

2. authentication set up

So far I'm calling reports via URL

http://[server_ip]:[port]/jasperserver/rest_v2/reports/reports/rep_pj_fakt_archiv.pdf?j_username=jasperadmin&j_password=jasperadmin&P_RIDIC_ID=1234&P_ROKMES=2015/01

Thanks,

Tomas