To test that it correctly authorises a valid user, prior to me extending it.
This only tests the happy path because simulating oAuth failures is going
to be quite hard at this stage.
The example JSON taken from GitHub's API documentation doesn't indicate that
`login` is the name of an organisation rather than a user. Change it to
something that looks more like an org, because it will make a test that I'm
about to add more readable. The endpoint name changes accordingly.