Amazon MWS Error SignatureDoesNotMatch - php

Question

we are trying to access the Amazon MWS Api but we just can't get it to work and we don't know why.
This is what we have tried so far:
require_once('.config.inc.php');
$base_url = "https://mws.amazonservices.de/Products/2011-10-01";
$method = "POST";
$host = "mws.amazonservices.de";
$uri = "/Products/2011-10-01";
$params = array(
'AWSAccessKeyId' => <our Key>,
'Action' => "GetLowestOfferListingsForASIN",
'SellerId' => <our ID>,
'SignatureMethod' => "HmacSHA256",
'SignatureVersion' => "2",
'Timestamp'=> gmdate("Y-m-d\TH:i:s.\\0\\0\\0\\Z", time()), //tried this with time()+7200 since our server is 2 hours back but we also accessed mws to get the time used there
'Version'=> "2011-10-01",
'MarketplaceId' => <our MpID>,
'ItemCondition' => 'new',
'ASINList.ASIN.1' => B00NN8LSXY );
// Sort the URL parameters
$url_parts = array();
foreach(array_keys($params) as $key)
$url_parts[] = $key . "=" . str_replace('%7E', '~', rawurlencode($params[$key]));
sort($url_parts);
// Construct the string to sign
$url_string = implode("&", $url_parts);
$string_to_sign = "POST\nmws.amazonservices.de\n/Products/2011-10-01\n" . $url_string;
// Sign the request
$signature = hash_hmac("sha256", $string_to_sign, AWS_SECRET_ACCESS_KEY, TRUE);
// Base64 encode the signature and make it URL safe
$signature = urlencode(base64_encode($signature));
$url = "https://mws.amazonservices.de/Products/2011-10-01" . '?' . $url_string . '&Signature=' . $signature;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 15);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
$response = curl_exec($ch);
//$parsed_xml = simplexml_load_string($response);
echo $response;
//return ($parsed_xml);
in the .config.inc.php file we added
all the Keys & IDs +
define('APPLICATION_NAME', '<our Firm>');
define('APPLICATION_VERSION', '1.0');
before we did all that we checked everything in MWS-Scratchpad but everything seems to be working there (on mws.amazon.de).
But we still get the SignatureDoesNotMatch Errorcode
<Message>The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details.</Message>
or this Errorcode:
<Message>Request signature is for too far in the future. Timestamp date: 2015-05-23T04:54:38.000Z. Currently, 10 percent of requests that are more than 15 minutes in the future will be rejected.</Message>
Hope someone can help we went through every other post and developer-guide about this - nothing seems to help

Answer 1

I had the same problem with it (among others).
The PHP reference and examples supplied by amazon has the answer buried deep within. The whole thing is a prime example of lasagna-code and reads like an insult to coders everywhere.
The API expects an HTTP POST with all the request data and a signiture made with your secret key. The sorting of the array and the url encoding standard changes the string to sign.
Amazon expects it sorted like this:
uksort($params, 'strcmp');
Forget the whole $url_parts part, it's messy. Use http_build_query() instead like this:
$url_string = http_build_query($params,'','&',PHP_QUERY_RFC3986);
Amazon expects RFC3986, so a space is encoded as '+', not '%20'. Also the timestamp should look like this:
'Timestamp' => gmdate("Y-m-d\TH:i:s\\Z", time()),
Good luck.

Answer 2

This happens when your machine's / Server's time is not correct. It happens to my servers sometimes when i reboot them. Just set the syncronization with time servers.