Although I am not familiar with Athena API requirements, I believe that you can use a component called HTTPConnector. It can send HTTP requests to a web APIs and receive responses. For more information about this component, please see the documentation:http://doc.cloveretl.com/documentation/UserGuide/index.jsp?topic=/com.cloveretl.gui.docs/docs/httpconnector.html
It is actually a usual requirement, therefore an example of the solution is already part of the CloverETL Designer installation. Go to Help -> CloverETL Examples and select any of the listed examples. It will load projects with all examples and you can then navigate to Basic Examples -> Graph -> WebServicesHTTP.grf in the Navigator pane on the left side of the Designer screen.
Hope this helps. Best Regards,