Trouble using API to subscribe to feeds

I’ve been using the API for a bunch of things successfully but am having trouble for some reason with the subscribeToFeed part – if I already have a session ID, do I need to use the login and password parameters, and if so, how are they formatted – I’ve tried most possibilities I can think of and am getting “Incorrect Usage” errors. Ideally, someone has the call to subscribetofeed in CURL format, so I can model my code? Thanks.

you can see android app source for complete example

login & password are most likely for the feed in case it’s password-protected (mirroring normal feed subscribe dialog)