Recently I found myself needing to get most recent content of a single file from a private Github repo.
It took me a while to figure out how to make it work using Guzzle, but once I got it, it was pretty simple to use.
One of the caveats is that, regardless of the type of error you might encounter when requesting a file from a private repo, the Github API always throws a 404 error. That can make it tricky to troubleshoot other kinds of errors (e.g., authentication, etc.)
Anyway, here’s a gist with the working code. You’ll need to modify this to suit your own situation, naturally. If you find this useful, let me know!