An example usage to grab the latest balance looks something like this:
P.S., I'm not officially affiliated with Jonathan Stark or his Jonathan's Card project in any way; I just really liked the idea of him making an API for this and had to play with it in my favourite language.
P.P.S., I've only spent a tiny bit of time writing this while taking a break from other work. Possible improvements include not using Strings and better error handling. It's possible but unlikely that I'll introduce these changes, so please know that pull requests are welcome and much appreciated.