我们计算的请求签名与您提供的签名不匹配.检查您的 AWS 秘密访问密钥和签名方法

我对亚马逊云科技 API 的测试请求返回并显示以下错误：

<ItemSearchErrorResponse xmlns="http://ecs.amazonaws.com/doc/2005-10-05/">
  <Error>
    <Code>SignatureDoesNotMatch</Code>
    <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>
  </Error>
  <RequestId>ebe90459-1abd-403e-bfec-6916ebe07e1f</RequestId>
</ItemSearchErrorResponse>

以下是我是如何得出这一点的：

<?php
$private_key = "XXXXXXXXXXXXXXXXXXXXXX";
$date = urlencode(date('Y-m-d'TH:i:s.Z'Z', time()));
$string_to_sign = "GET webservices.amazon.com /onca/xml/ AWSAccessKeyId=XXXXXXXXXXXXXXXXXXXXXXXA&Keywords=Rocket&Operation=ItemSearch&SearchIndex=Toys&Service=AWSECommerceService&Timestamp=".$date."";
$signature = urlencode(base64_encode(hash_hmac("sha256",$string_to_sign, $private_key, True)));
$url = "http://webservices.amazon.com/onca/xml?AWSAccessKeyId=XXXXXXXXXXXXXXXXXXXXXXXX&Keywords=Rocket&Operation=ItemSearch&SearchIndex=Toys&Service=AWSECommerceService&Timestamp=".$date."&Signature=".$signature."";
header("Location: ".$url."");
?>

我基本上想要直接在 url 中签名的 REST 请求（因此是标头函数），但让我陷入了错误。我仔细检查了我的访问ID和密钥，所以我知道它们不是导致问题的原因。这不是生成签名的正确方法吗？