问翻译君API 接口鉴权总是错误？

<?php

define("WAY",            "TextTranslate");
define("PLACE",          "gz");
define("URL",            "https://tmt.api.qcloud.com/v2/index.php");
define("SEC_ID",         "XX");
define("SEC_KEY",        "XX");

//翻译入口
function translate($sourceText, $source, $target)
{
    $tm=time();
    $nc=rand(10000,99999);
    $args = array(
        'Action'=>WAY,
        'Nonce'=>$nc,
        'Region'=>PLACE,
        'SecretId'=>SEC_ID,
        'Timestamp'=>$tm,
        'sourceText' => $sourceText,
        'source' => $source,
        'target' => $target
    );
    $args['Signature'] = buildSign($tm,$nc);

    $url=URL.'?';
    foreach ($args as $key=>$value)
    {
        $url.=$key.'='.urlencode($value).'&';
    }
    $url=substr($url,0,strlen($url)-1);

    $ret = doCurlGetRequest($url);
    $ret = json_decode($ret, true);
    echo var_dump($ret);
}

//生成签名串
function buildSign($time,$nonce)
{
    $pars = array(
        'Action'=>WAY,
        'SecretId'=>SEC_ID,
        'Timestamp'=>$time,
        'Nonce'=>$nonce,
        'Region'=>PLACE
    );
    ksort($pars);
    $reqStr='';
    foreach ($pars as $key => $value)
    {
        $reqStr.=$key.'='.$value.'&';
    }
    $reqStr = substr($reqStr,0,strlen($reqStr)-1);

    $srcStr ='GETtmt.api.qcloud.com/v2/index.php?'.$reqStr;
    $signStr = base64_encode(hash_hmac('sha1', $srcStr, SEC_KEY, true));
    return $signStr;
}