检查是否在PHP中设置变量以分割代码

Question

I have a PHP file that can be directly accessed in Browser and it also recieves notifications from Stripe payment gateway. The file starts with:

<?php

error_reporting(E_ERROR | E_PARSE);

require_once('../stripe/init.php');

\Stripe\Stripe::setApiKey("XXXXXXXXXXXXXXXXXXX");

$body = @file_get_contents('php://input');
$event_json = json_decode($body);

if(empty($event_json))
    exit();

$event_id = $event_json->id;
$event = \Stripe\Event::retrieve($event_id);

//So on......

?>

How do I check if execution is from browser or Stripe?

Like Should I check empty $event_json or $event_id ?

I want to write code as:

if(check_if_executed_from_Stripe)
   do_this
else
   do_that