Facebook graph api 我无法在我的网站中添加facebook登录。。它重定向并再次显示登录按钮，，

当我点击login按钮时，它会重定向到fb登录页面，现在在给出email_id和paasword后，它会提示允许访问example.com想要的pern任务，在允许它重定向到重定向url后，它不会显示任何用户信息。。它再次显示登录按钮。。。它似乎返回了session false

我有大麻烦了。。。无法解决这个问题。。在这方面请帮忙好吧，不需要帮忙。。我自己解决了。

<?php 
session_start();


require_once( 'Facebook/HttpClients/FacebookHttpable.php' );
require_once( 'Facebook/HttpClients/FacebookCurl.php' );
require_once( 'Facebook/HttpClients/FacebookCurlHttpClient.php' );
require_once( 'Facebook/Entities/AccessToken.php' );
require_once( 'Facebook/Entities/SignedRequest.php' );
require_once( 'Facebook/FacebookSession.php' );
require_once( 'Facebook/FacebookRedirectLoginHelper.php' );
require_once( 'Facebook/FacebookRequest.php' );
require_once( 'Facebook/FacebookResponse.php' );
require_once( 'Facebook/FacebookSDKException.php' );
require_once( 'Facebook/FacebookRequestException.php' );
require_once( 'Facebook/FacebookOtherException.php' );
require_once( 'Facebook/FacebookAuthorizationException.php' );
require_once( 'Facebook/GraphObject.php' );
require_once( 'Facebook/GraphSessionInfo.php' );

use Facebook\HttpClients\FacebookHttpable;
use Facebook\HttpClients\FacebookCurl;
use Facebook\HttpClients\FacebookCurlHttpClient;
use Facebook\Entities\AccessToken;
use Facebook\Entities\SignedRequest;
use Facebook\FacebookSession;
use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookRequest;
use Facebook\FacebookResponse;
use Facebook\FacebookSDKException;
use Facebook\FacebookRequestException;
use Facebook\FacebookOtherException;
use Facebook\FacebookAuthorizationException;
use Facebook\GraphObject;
use Facebook\GraphSessionInfo;

FacebookSession::setDefaultApplication('abc','xyz');

$required_scope     = 'public_profile, email';

// login helper with redirect_uri
$helper = new FacebookRedirectLoginHelper( 'http://www.example.com/' );

try {
  $session = $helper->getSessionFromRedirect();
} catch(FacebookRequestException $ex) {
  // When Facebook returns an error
} catch(\Exception $ex) {
  // When validation fails or other local issues
}



if ($session){ //if we have the FB session
    $up = (new FacebookRequest($session, 'GET', '/me'))->execute()->getGraphObject(GraphUser::className());

    echo $up->getId();
    echo $up->getName();
    echo $up->getFirstName();
    echo $up->getMiddleName();
    echo $up->getLastName();
    echo $up->getLink();
    echo $up->getBirthday();
    echo $up->getLocation();
}
else
{
   echo '<a href="' . $helper->getLoginUrl(array( 'scope' => $required_scope )) . '">Login to FB</a>';
}
?>