Invite people to Apple TestFlight to test iOS app using AppStore API

Question

I found that Apple has API for accessing TestFlight:

https://developer.apple.com/documentation/appstoreconnectapi/send_an_invitation_to_a_beta_tester

But there is no sample and no document for how to authenticate to this API and send, I wish there was a PostMan or Curl sample.

Anybody knows how to code this in PHP?