I have been working with 3rd party APIs for a very long time. Each time I usually either pull in their SDK, if there is one available, or I build a wrapper around their API and work from there.
I have also built a handful of PHP SDKs for APIs that do not have SDKs in PHP, or the ones provided were somewhat sub par - or I simple wanted to do it my way.
I have recently built a new package called https://github.com/JustSteveKing/http-auth-strategies which is simple and tested way to build authentication headers for API calls.
We can then access all methods from the AbstractResource allowing us to fluently build our API calls, in a structured and clean way.