I am an administrator (manager role) of a Facebook Group. I created an app, and stored its id and secret.

I want my app to be able to post something on the Facebook group's feed. But when I attempt to post, I get the error 190 Invalid OAuth access token signature, even though I able to successfully obtain the access_token with publish_stream and offline_access scopes. It has the form of NNNNNNNNNNNNNNN|XXXXXXXXXXXXXXXXXXXXXXXXXXX, where N is a number (15) and X is a letter or a number (27).

What should I do more to get this accomplished? Here is the code I am using:

public static function postToFB($message, $image, $link) {

    //Get App Token
    $token = self::getFacebookToken();

    // Create FB Object Instance
    $facebook = new Facebook(array(
        'appId'  => self::fb_appid,
        'secret' => self::fb_secret,
        'cookie' => true
    ));

    //$token = $facebook->getAccessToken();

    //Try to Publish on wall or catch the Facebook exception
    try {
        $attachment = array('access_token' => $token,
                'message' => $message,
                'picture' => $image,
                'link' => $link,
                //'name' => '',
                //'caption' => '',
                'description' => 'More...',
                //'actions' => array(array('name' => 'Action Text', 'link' => 'http://apps.facebook.com/xxxxxx/'))
            );

        $result = $facebook->api('/'.self::fb_groupid.'/feed/', 'post', $attachment);
    } catch (FacebookApiException $e) { //If the post is not published, print error details
        echo '<pre>';
        print_r($e);
        echo '</pre>';
    }
}

Code which returns the token

//Function to Get Access Token
public static function getFacebookToken($appid = self::fb_appid, $appsecret = self::fb_secret) {
    $args = array(
        'grant_type' => 'client_credentials',
        'client_id' => $appid,
        'client_secret' => $appsecret,
        'redirect_uri' => 'https://www.facebook.com/connect/login_success.html',
        'scope' => 'publish_stream,offline_access'
    );

    $ch = curl_init();
    $url = 'https://graph.facebook.com/oauth/access_token';
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_HEADER, false);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $args);

    try {
        $data = curl_exec($ch);
    } catch (Exception $exc) {
        error_log($exc->getMessage());
    }
    return json_encode($data);
}

If I uncomment $token = $facebook->getAccessToken(); in the posting code, it gives me yet another error (#200) The user hasn't authorized the application to perform this action.

The token I get using developers.facebook.com/tools/explorer/ is of another form, much longer and with it I am able to post to the group page feed.

How do I do it without copy/paste from Graph API Explorer and how do I post as a group instead of posting as a user?

Thanks.