We prepped them ahead of time telling them that they would need to produce an HTTP API that accepted requests and returned a response compiled from multiple HTT

We prepped them ahead of time telling them that they would need to produce an HTTP API that accepted requests and returned a response compiled from multiple HTTP endpoints. It's basically an orchestration layer, and I've done similar things in production many times. ("If we exposed X to the clients, we could allow action Y. Would action Y contribute to our goal of Z?" Instead of building a highly performant correct solution, we would do an on the fly derivation of the data needed, launch it for 5% and see the experiment results.) It was for all candidates, meant to test ability to understand a problem and prototype a solution quickly. Edit: most candidates did Java/Scala/Python/Ruby.