@jlrdw It's procedural code. Not even remotely OO..
It could probably be wrapped up in a class, and there's really so little code involved it would probably make sense to simply copy/paste it into a class that can be autoloaded.
Based on the quality of the code though, I'd seriously question whether or not to use this service at all. They have several other repos for various other languages, none of which have any code. Makes me think the service is probably somewhat poorly implemented in php and while they intended to provide SSO libraries for it in other languages (.net, java, python, etc) they haven't gotten around to doing so in 4+ years.
Maybe it's just me, but that doesn't inspire a lot of confidence for me.