Understanding Azure website auto-scale magic

I was helping out a consumer of Have I been pwned? (HIBP) earlier today as they were trying to build up a profile of the pwnage state of their client base. This mean firing a heap of requests at the API so that they could assess a vey large number of accounts. I’m always interested in how far this service can be stretched and indeed what the thresholds are before Azure starts applying auto-scale magic.