PHP key-restricted content with GET. If high security is needed it would be better to use POST.

PHP Key Restriction GET

<?php

/**
 Sample to get a url variable through GET method

 Example URL: ../sample.php?apikey=MY_KEY
*/

// Define the API key here
$APIKey = 'MY_KEY'; // this is the key that the app has to send on the URL

// Obtain the GET variable apikey
$getAPIKey = $_GET['apikey']; // this is the key sent by the app on the URL

// Check if keys match each other
if ($APIKey == $getAPIKey) {
  // Show JSON data here.
	echo "Show data.";
} else {
	// Do not show JSON data.
	echo "Do not show data.";
}


?>