This is a fairly simple if somewhat time-consuming problem, as it mostly requires you to be able to quickly learn a new API within the time constraints of an interview. There really isn't much to say about the solution as anyone should be able to do it. However, it was one of the most fun interview questions I've ever gotten. I don't know how common it is, as I believe the interviewer asked me this question mostly because I said I liked working with APIs when I was introducing myself. But that means that my interviewer was playing to my interests, so take it as a plus that the team really wants to get to know you as a person and isn't only looking at your technical skills!