Where can I get a description / sample [how to make] API (in any form, but OpenAPI is better) for Google reCAPTCHA?

Question

API

I want to attach Google reCAPTCHA to a project on the REST API, and to my surprise (the task is a typical one) I did not find any intelligible description either on the swaggerhub or anywhere else.

Where to get?

Or if someone writes in the form of request-response - it will be cool :)

Thank you.