Ah. I have an app name, created a client key, I'd previously read through the docs to establish what I need to do to create an authentication token, and what to expect as a response. And then curl tells me https is disabled or not supported by the version of libcurl I have installed on my Raspberry Pi.
curl: (52) Empty reply from server
> curl: (1) Protocol " https" not supported or disabled in libcurl
No worries, I'll fiddle some more. ;)