使用PHP POST对Amazon AMS API进行身份验证

我从SO的其他地方获得了这段代码。它的工作原理与宣传的一样。然而，我正试图用POST而不是GET做同样的事情，这显然是AMS建议的，也是这个特定调用在AMS Scratchpad上的放置方式。

适用于GET 的代码

<?php
$param = array();
$param['AWSAccessKeyId']   = 'YourAccessKeyID'; 
$param['Action']           = 'GetLowestOfferListingsForASIN'; 
$param['SellerId']         = 'YourSellerID'; 
$param['SignatureMethod']  = 'HmacSHA256';  
$param['SignatureVersion'] = '2'; 
$param['Timestamp']        = gmdate("Y-m-d'TH:i:s.''0''0''0''Z", time());
$param['Version']          = '2011-10-01'; 
$param['MarketplaceId']    = 'YourMarketplaceID'; 
$param['ItemCondition']    = 'new';
$param['ASINList.ASIN.1']  = 'B00C5XBAOA';
$secret = 'YourSecretKey';
$url = array();
foreach ($param as $key => $val) {
    $key = str_replace("%7E", "~", rawurlencode($key));
    $val = str_replace("%7E", "~", rawurlencode($val));
    $url[] = "{$key}={$val}";
}
sort($url);
$arr   = implode('&', $url);
$sign  = 'GET' . "'n";
$sign .= 'mws.amazonservices.com' . "'n";
$sign .= '/Products/2011-10-01' . "'n";
$sign .= $arr;
$signature = hash_hmac("sha256", $sign, $secret, true);
$signature = urlencode(base64_encode($signature));
$link  = "https://mws.amazonservices.com/Products/2011-10-01?";
$link .= $arr . "&Signature=" . $signature;
echo($link); //for debugging - you can paste this into a browser and see if it loads.
$ch = curl_init($link);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type: application/xml'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE); 
$response = curl_exec($ch);
$info = curl_getinfo($ch);
curl_close($ch);
echo('<p>' . $response . '</p>');
print_r('<p>' . $info . '</p>');
?>

不适用于POST 的代码

<?php
$post = '';
$param = array();
$param['AWSAccessKeyId']   = 'YourAccessKeyID'; 
$param['Action']           = 'GetLowestOfferListingsForASIN'; 
$param['SellerId']         = 'YourSellerID'; 
$param['SignatureMethod']  = 'HmacSHA256';  
$param['SignatureVersion'] = '2'; 
$param['Timestamp']        = gmdate("Y-m-d'TH:i:s.''0''0''0''Z", time());
$param['Version']          = '2011-10-01'; 
$param['MarketplaceId']    = 'YourMarketplaceID'; 
$param['ItemCondition']    = 'new';
$param['ASINList.ASIN.1']  = 'B00C5XBAOA';
$secret = 'YourSecretKey';
$url = array();
foreach ($param as $key => $val) {
    $key = str_replace("%7E", "~", rawurlencode($key));
    $val = str_replace("%7E", "~", rawurlencode($val));
    $url[] = "{$key}={$val}";
}
sort($url);
$arr   = implode('&', $url);
$sign  = 'POST' . "'n";
$sign .= 'mws.amazonservices.com' . "'n";
$sign .= '/Products/2011-10-01' . "'n";
$sign .= $arr;
$signature = hash_hmac("sha256", $sign, $secret, true);
$signature = urlencode(base64_encode($signature));
$post .= $arr . "&Signature=" . $signature;
echo $post;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,"https://mws.amazonservices.com/Products/2011-10-01");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, '$post');
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type: application/xml'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE); 
$response = curl_exec($ch);
$info = curl_getinfo($ch);
curl_close($ch);
$response = simplexml_load_string($response);
print_r($response);
//print_r($info);
?>

我得到以下回复：

(
    [Error] => SimpleXMLElement Object
        (
            [Type] => Sender
            [Code] => InvalidParameterValue
            [Message] => Either Action or Operation query parameter must be present.
        )
    [RequestID] => b6d5ee02-6ace-4482-92b7-xxxxxxxxxx
)

我认为我在签名验证方面出了问题。如有任何帮助，我们将不胜感激。