使用Facebook PHP SDK进行身份验证时出现问题

I am trying out a bit of Facebook PHP SDK. Here is my code :

<?php
    /* Connect to facebook link. */
    require_once('./fb/facebook.php');


    $facebook = new Facebook(array(
        'appId' => '189152054469765',
        'secret' => 'ccd2d3e7986fb1ij4c9e41018327db67',
                'cookie'=>true
    ));
echo $facebook->api('/me');
?>

On running the file, I am getting the error: Uncaught OAuthException: An active access token must be used to query information about the current user. I've seen the above code working for all in all tutorials. I am logged into facebook and given permissions for email and publish_stream to my app.

You need to perform oauth authentication (basically redirects with token exchange).

So you check for $user = $facebook->getUser();

And if not, you click on $facebook->getLoginUrl();