Support for GitHub webhook to update local repository utilizing secret key matching

github_webhook_update.php

<?php
	//polyfill for missing hash_equals
	if(!function_exists('hash_equals'))
	{
	    function hash_equals($str1, $str2)
	    {
	        if(strlen($str1) != strlen($str2))
	        {
	            return false;
	        }
	        else
	        {
	            $res = $str1 ^ $str2;
	            $ret = 0;
	            for($i = strlen($res) - 1; $i >= 0; $i--)
	            {
	                $ret |= ord($res[$i]);
	            }
	            return !$ret;
	        }
	    }
	}

	$signatureHeader = $_SERVER['HTTP_X_HUB_SIGNATURE'];
	$requestBody = file_get_contents('php://input');
	
	$signature = "sha1=" . hash_hmac('sha1', $requestBody, 'your secret key here');

	if(hash_equals($signatureHeader, $signature))
		exec('cd /path/to/your/repo git reset --hard HEAD && git pull');
	else
		echo "Sorry pal, can't do that!";
?>