Using Facebook Single Sign-On

Question

Hi i want to built single sign on using with facebook api and secret key. i am using below code in the index.php:

<?php

define('FACEBOOK_APP_ID', 'myapikey');
define('FACEBOOK_SECRET', 'secretkey');

function get_facebook_cookie($app_id, $application_secret) {
    $args = array();
    parse_str(trim($_COOKIE['fbs_' . $app_id], '\\"'), $args);
    ksort($args);
    $payload = '';
    foreach ($args as $key => $value) {
        if ($key != 'sig') {
            $payload .= $key . '=' . $value;
        }
    }
    if (md5($payload . $application_secret) != $args['sig']) {
      return null;
    }
    return $args;
}

$cookie = get_facebook_cookie(FACEBOOK_APP_ID, FACEBOOK_SECRET);
echo 'The ID of the current user is ' . $cookie['uid'];

?>

for connect facebook login i am using below code:

<?php if ($cookie) { ?>
     Your user ID is <?= $cookie['uid'] ?>
<?php } else { ?>
<fb:login-button perms="email"></fb:login-button>
<?php } ?>


   <div id="fb-root"></div>
       <script src="http://connect.facebook.net/en_US/all.js"&gt;&lt;/script&gt;
       <script>
             FB.init({appId: '<?= FACEBOOK_APP_ID ?>', status: true,
                     cookie: true, xfbml: true});
                                                              FB.Event.subscribe('auth.login', function(response) {

                  window.location.reload();
                                                         });
       </script>

when i login to facebook through mysite it want let me login on my site. i want that if i login to facebook through my site. after logged in if i have any account on my site it should be logged in

can any one solve it