issue: OAuth oauth_problem="parameter_absent: oauth_signature", realm="yahooapis.com"

according to yahoo API official online document, i exploring oauth with yahoo & i want to grab yahoo contacts by using url: http://social.yahooapis.com/v1/user/GUID/contacts
i have got some information as step 5 of oauth show in http://developer.yahoo.com/oauth/guide/oauth-refreshaccesstoken.html
And now, i'm using CURL to load: http://social.yahooapis.com/v1/user/GUID/contacts to grab contacts list
my code here:

//starting load contact
$get_contacts_url="http://social.yahooapis.com/v1/user/".$xoauth_yahoo_guid."/contacts";

$auth_header=array(
    'Authorization:OAuth',
    'realm:yahooapis.com',
    'oauth_consumer_key:dj0yJmk9eTYxaGMxczNqUW1iJmQ9WVdrOWJGZEdZVkpDTldNbWNHbzlNVFU1TXprMU56UTJNZy0tJnM9Y29uc3VtZXJzZWNyZXQmeD1jZQ--',
    'oauth_nonce:abc',
    'oauth_signature_method:PLAINTEXT',    //HMAC-SHA1
    'oauth_timestamp:'.time(),
    'oauth_token:'.$_SESSION['oauth_token'],
    'oauth_signature:387892fe58f962859758bbb278dd7a4c37bd4dd6&'.$_SESSION['oauth_token_secret'],
    'oauth_version:1.0'
    );

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $get_contacts_url);
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt ($ch, CURLOPT_HTTPHEADER, $auth_header);

echo curl_exec ($ch);
curl_close($ch);

PHP:

But i still get issue: Please provide valid credentials. OAuth oauth_problem="parameter_absent: oauth_signature", realm="yahooapis.com"

People can help me? I wondering this message. I dont any treat with this problem.