问接口鉴权 code: 4100, message: "身份认证失败，用户身份验证失败",？

接口鉴权 按文档写的 获取视频时长 为什么总是 code: 4100, message: "身份认证失败，用户身份验证失败",

$secretId = "******";

$secretKey = "*********";

$param["Action"] = "DescribeInstances";

$param["SecretId"] = $secretId;

$param["Timestamp"] = time();

$param["Nonce"] = rand(10000,99999);

$param["Region"] = "gz";

$param["instanceIds.0"] = "ins-09dx96dg";

//$param["SignatureMethod"] = "HmacSHA256";

//$param["Version"] = "2017-03-12";

$param["limit"] = 20;

$param["offset"] = 0;

ksort($param);

//dump(PHP_EOL);

$signStr = "https://GETcvm.api.qcloud.com/v2/index.php?";

//$signStr = "";

foreach ( $param as $key => $value ) {

$signStr = $signStr . $key . "=" . $value . "&";

}

$signStr = substr($signStr, 0, -1);

$signature = urlencode(base64_encode(hash_hmac('sha1', $signStr, $secretKey, true)));

$url = "https://vod.api.qcloud.com/v2/index.php?Action=GetVideoInfo&fileId={$fileid}&Signature={$signature}&SecretId={$secretId}&Region=gz&Timestamp={$param["Timestamp"]}&Nonce={$param["Nonce"]}";

//echo $url;