Intuit discoverAndAdd method returns Authentication error in PHP

Question

I am calling the discoverAndAdd method of intuit. According to the specification mentioned here. I am getting the Authorization headers using the below code:

IntuitAggCatHelpers::GetOAuthTokens(&$oauth_token, &$oauth_token_secret);
    $signatures = array('consumer_key' => OAUTH_CONSUMER_KEY,
             'shared_secret' => OAUTH_SHARED_SECRET,
                'oauth_token' => $oauth_token,
                'oauth_secret' => $oauth_token_secret);

        $oauthObject = new OAuthSimple();
        $oauthObject->reset();
        $name='institutions';
        $result = $oauthObject->sign(array(
                'path' => FINANCIAL_FEED_URL . 'v1/' . $name.'/100000/logins',
                'parameters' => array('oauth_signature_method' => 'HMAC-SHA1',
                    'Host' => FINANCIAL_FEED_HOST),
                'signatures' => $signatures));

And then I am calling the discoverAndAdd method using the below code:

$xmlStr='<InstitutionLogin xmlns="http://schema.intuit.com/platform/fdatafeed/institutionlogin/v1">
    <credentials>
        <credential>
            <name>Banking Userid</name>
            <value>demo</value>
        </credential>
        <credential>
            <name>Banking Password</name>
            <value>go</value>
        </credential>
    </credentials>
</InstitutionLogin>';

define('XML_PAYLOAD', $xmlStr);
define('XML_POST_URL', $result['signed_url'];

/**
 * Initialize handle and set options
 */
$ch = curl_init();
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'POST');
curl_setopt($ch, CURLOPT_URL, XML_POST_URL);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, XML_PAYLOAD);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
                                   'Content-type: application/xml', 
                                   'Content-length: ' . strlen(XML_PAYLOAD)
                                 ));

$result = curl_exec($ch);

It is supposed to return some challenge headers like this question

but I am getting the below headers :

HTTP/1_1_401_Code:ApplicationAuthenticationFailed,Type:SYSTEM Date:_Tue,_03_Dec_2013_08:10:17_GMT intuit_tid:_gw-bb793220-51cd-420b-8502-c4674db06611 Content-Type:_text/plain Content-Length:_0

The status code tells that there is some problem in authentication but the authentication token is working fine for GetAll method.