How to access incoming request object in Custom script in the absence of file_get_contents

Summary: Need suggestions on how to read incoming POST request data from within a custom script.

Content (required): We have a custom script that is being called as a REST API from a third party application. We have been using file_get_contents('php://input') to read the POST json contents as raw data but since file_get_contents is no more supported we are stuck. I need some suggestions on how to read incoming request data from within a custom script without using file_get_contents. The request is a POST method and I understand that $_POST will result in a blank array for json content.