Calling External API from ABAP having API Key

We have to call one API from ABAP. External party gives us the https URL for a get method and also provide separately one API key. So we do not know How to send API key when calling API from ABAP. The url that is given to us as like

https://testbox-sample.gst.in/api/DRT/search

When searched in the forum we are able to get how to call one external API through cl_http_client=>create_by_url using username and password. But our External having API key and how to send it during API call from ABAP is our problem.

So please help us to get info related to our problem .