Make a signed query with Amazon API MWS

Question

I'm trying to make a signed request for Seller Amazon Web Services (MWS). I'm using a script from here: Converting amazon MWS scratchpad queries to API calls

But I don't know why I've got an error: "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."

So here is my script:

define ("AWS_ACCESS_KEY_ID", "xxxxx");
define ("MERCHANT_ID", "xxxxx");
define ("MARKETPLACE_ID", "xxxxx");
define ("AWS_SECRET_ACCESS_KEY","xxxxx");

$base_url = "https://mws.amazonservices.fr/Products/2011-10-01";
$method = "POST";
$host = "mws.amazonservices.fr";
$uri = "/Products/2011-10-01";

function amazon_xml($searchTerm) {

$params = array(
'AWSAccessKeyId' => AWS_ACCESS_KEY_ID,
'Action' => "GetLowestOfferListingsForSKU",
'SellerId' => MERCHANT_ID,
'SignatureMethod' => "HmacSHA256",
'SignatureVersion' => "2",
'Timestamp'=> date("Y-m-d\TH:i:s.\\0\\0\\0\\Z", time()),
'Version'=> "2011-10-01",
'MarketplaceId' => MARKETPLACE_ID,
'Query' => $searchTerm,
'ItemCondition'=> "New",
'ExcludeMe' => "false");


// 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 = str_replace("%7E", "~", implode("&", $url_parts));
$string_to_sign = "POST\nmws.amazonservices.fr\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
$signature = rawurlencode(base64_encode($signature));

$url = "https://mws.amazonservices.fr/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);

return ($parsed_xml);
}

I don't understand what's going wrong If someone could help....

Thanks in advance !

Answer 1

You got an issue when you are signing the string..try this

$url_parts = array();
foreach(array_keys($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 = "GET\nmws.amazonservices.com\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.com/Products/2011-10-01" . '?' . $url_string . "&Signature=" . $signature;

its working for me...Hopes this helps

Answer 2

Make sure that when using cURL you set the method to "GET", in the above example change to

$method = "GET";

and it should work.