publish post on Facebook wall when the user views the node

I want to publish a post on Facebook when the user views the node without interrupting the user
For this I setup an IFRAME facebook application and directed to my website
on hook_view function I called this

$path = 'XXX';
require_once $path;
$appapikey = 'XXX';
$appsecret = 'XXX';
$facebook = new Facebook($appapikey, $appsecret);
$user_id = $facebook->require_login();

if (!$facebook->api_client->users_hasAppPermission("publish_stream")){  
 
 }
else
{
	$message = 'XXX'; 
	$facebook->api_client->stream_publish($message);
}

the problem is, how should I request user to grant extended permission ('publish_stream')?
can anyone please help me with this.
Any suggestions would be appreciated!