Amazon Product Advertising APIの署名認証ルーチンを書いてみた

function addAuthSig($url, $secret){
        $urlArr = parse_url($url);
        parse_str($urlArr["query"], $paramArr);
        $paramArr['Timestamp'] = gmdate("Y-m-d\TH:i:s\Z");
        ksort($paramArr);

        $paramStr = "";
        foreach( $paramArr as $key => $value ){
                $paramStr .= $key ."=" . rawurlencode($value) . "&";
        }
        $strToSign = "GET\n${urlArr['host']}\n${urlArr['path']}\n" . rtrim($paramStr, '&');
        $sig = rawurlencode( base64_encode( hash_hmac("sha256", $strToSign, $secret, true) ) );

        return  $urlArr['scheme'] . "://" . $urlArr['host'] . $urlArr['path'] . '?' . $paramStr
                 . "Signature=" . $sig;
}