Open Graph User variable gets null after authorization - php

Question

I am using Facebook's Open Graph API to import a user's images from his/her account.
But when I click on the login button and it opens the URL, after authorization it asks me again to login.
Here is my index.php:
<?php
ini_set("display_errors",0);
if ( !defined('ABSPATH') )
require_once '../../../../wp-load.php';
include_once __DIR__."/fbmain.php";
include_once __DIR__."/facebook.php";
if(!session_id())session_start();
global $fbSiteUrl;
/*$base_url = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS']!='off') ? 'https://' : 'http://';
$base_url .= $_SERVER['HTTP_HOST'];*/
$fbSiteUrl = COO_PLUGIN_URL."/create-own-object/plugin-facebook";//$base_url.substr(__DIR__,strpos(__DIR__,'/phase2-newer'));
/*if(isset($_GET['logout']) && $_GET['logout']=='yes'){
$user = null;
$facebook->logoutFromSite();
}*/
if (!$user){
?>
<div class="facebook_login_box" id='fbLoginBtn'>
<div class="text-center">
<img src="<?php echo $fbSiteUrl; ?>/Images/facebook_logo.png" alt="" >
</div>
<div class="fb_login">
<button type="button" class="fb_login_btn" style="margin-right: 90px;" onclick="authoriseToSocialMedia('<?php echo $loginUrl; ?>');">Login</button>
</div>
</div>
<?php
}// else { ?>
<!-- <div class="right_side">
</div> -->
<?php //} ?>
<img src="<?php echo $fbSiteUrl; ?>/Images/folder_fb.png" style="display:none;">
<!-- all time check if user session is valid or not -->
<?php
if ($user) {
?>
<div id ='FBcontent'>
<form id ='FBcontentFrm' method="post" action="index.php">
<div class="folderset" id="folderList">
<!-- Data retrived from user profile are shown here -->
<?php
$albums = $facebook->api("/me/albums");
foreach($albums['data'] as $album){
?>
<div class="box">
<a href="javascript:void(0);" onclick="showAlbum('<?php echo $album['id']; ?>')">
<img src="<?php echo $fbSiteUrl; ?>/Images/folder_fb.png">
<div style="clear: both;"></div><?php echo $album['name']; ?>
</a>
</div>
<?php
}
?>
<div class="clearfix"></div>
</div>
<div id="fbhtmlImage">
<!-- Album images are being loaded here. -->
</div>
</form>
<script>
if((this.window.focus() || !(this.window.closed)) && window.opener != null)
{
window.opener.document.getElementById('facebook_content').innerHTML = document.getElementById('FBcontent').innerHTML;
window.opener.document.getElementById("fbLoginBtn").style.visibility="hidden";
this.window.close();
}
</script>
</div>
<?php } ?>
<script type="text/javascript">
function backToAlbums(){
$('#fbhtmlImage').hide();
$('#fbmodal-footer').hide();
$('#folderList').show();
}
function showAlbum(albumId){
$('#loader_img').show();
<?php global $fbSiteUrl;?>
$('#folderList').hide();
var fbhtml = '';
fbhtml += '<div class="image_list addimage_box_col">\
<div class="row">\
<div class="col-lg-2 col-sm-3 col-xs-6">\
<a class="pink_btn" href="javascript: void(0);" onClick="backToAlbums();">Back</a>\
</div>\
</div>\
<div class="clearfix"></div>\
</div>';
$.ajax({
type: "GET",
url: "<?php echo $fbSiteUrl; ?>/fbphotos.php",
data: { albumId: albumId }
}).done(function(response) {
var response = jQuery.parseJSON(response );
var showBtn = false;
fbhtml += "<div class='image_list addimage_box_col'>\
<div class='row'>";
if(response['data'].length>0)
{
for(var x=0; x<response['data'].length; x++){
fbhtml += '<div class="col-lg-2 col-sm-3 col-xs-6" style="padding-top: 15px;"><div class="checkbox_left">';
fbhtml += '<input type="checkbox" class="css-checkbox" id="facebook_'+x+'" name="facebook[]" value="'+response['data'][x]['source']+'" />';
fbhtml += '<label class="css-label radGroup1" for="facebook_'+x+'"></label>';
fbhtml += '</div>';
fbhtml += '<div class="image_thumb">';
fbhtml += '<img class="bdr img-responsive center-block" src="'+response['data'][x]['source']+'" />';// style="width:100px !important; height:100px !important;" />';
fbhtml += '</div></div>';
showBtn = true;
}
}
else
{
fbhtml += '<div class="image_thumb">';
fbhtml += 'There are no image(s) in this album.';
fbhtml += '</div>';
}
fbhtml += "<input type='hidden' name='fb_copy' value='Copy Selected Files'>\
</div>\
<div class='row'>";
fbhtml += '<div class="col-lg-2 col-sm-3 col-xs-6" style="padding-bottom: 10px; padding-top: 10px;">';
if(showBtn == true)
{
fbhtml += "<input type='button' class='pink_btn' name='fb_copy' value='Copy Selected Files' onclick='moveImages($(\"#FBcontentFrm\").serialize())' />";
}
fbhtml += "</div>\
</div>\
</div>";
$('#fbhtmlImage').html(fbhtml);
$('#fbhtmlImage').show();
$('#loader_img').hide();
});
}
</script>
<script>
/*
function moveImages(){
$.post(SiteURL+"wp-content/themes/mydomain/moveSelectedImages.php", $("#FBcontent").serialize(),function(data){
alert(data);
} );
}*/
</script>