Yahoo Japan Shop API :Service Requires Authentication

Question

I have tried to register product into my shop by using the following code but it return "Service Requires Authentication"

What I have tried is

<?php

$api = 'https://circus.shopping.yahooapis.jp/ShoppingWebService/V1/editItem';
$appid = 'My App ID';
$params = array(
   'seller_id' => 'dicdicdic',
   'item_code' => '123456789',
   'path'  => 'TOPS',
   'name' => 'Soro Product 1',
   'price' => '999'
);

$ch = curl_init($api);
curl_setopt_array($ch, array(
    CURLOPT_POST           => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_USERAGENT      => "Yahoo AppID: $appid",
    CURLOPT_POSTFIELDS     => http_build_query($params),
));

$result = curl_exec($ch);
curl_close($ch);
?>
<pre>
<?php echo htmlspecialchars(
             print_r(new SimpleXMLElement($result), true)
           ) ?>
</pre>

I could not find any solution. Please help!!!