$ cat post_debug.php 
<?php

if (isset($_POST)) {
	$logData='================'.PHP_EOL;
	$logData.=date("Y-m-d H:i:s").PHP_EOL;
	$logData.=print_r($_POST, true).PHP_EOL;
	
	if (!empty($_POST)) {
		foreach ($_POST as $key=>$value) {
			@$jsonDec=json_decode($value,true);
			if (is_array($jsonDec)) {
				$logData.='----------------'.PHP_EOL;
				$logData.=print_r($jsonDec,true).PHP_EOL;
			}
		}
	}
	$logData.='================'.PHP_EOL;
	file_put_contents('/tmp/post_debug.log',$logData,FILE_APPEND);
}