Hey @gilles, I have not personally done much with this sort of thing. However, I did encounter it once and I do have a video where I talk a bit about this in a real world context (setting up Amazon Product Search API).
That video can be found here:
Encrypting a signature for authentication to this API is discussed briefly. This is a LOT of content to wade through for that, but I do touch on it (somewhere around 30 - 45 minutes in is probably where this happens.
