Facebook SDK returned an error: You must provide an access token. Php Facebook Api

问题

<?php

require_once 'Facebook/autoload.php';
require_once 'Facebook/Authentication/AccessToken.php';
$fb = new Facebook\Facebook([
  'app_id' => '2452542542fsrgrgrg',
  'app_secret' => '5245dffhdhr5535353535',
  'default_graph_version' => 'v2.2',
  ]);

$linkData = [
  'link' => 'http://www.example.com',
  'message' => 'User provided message',
  ];
$helper = $fb->getRedirectLoginHelper(); 
try {
  $accessToken = $helper->getAccessToken(); 
  // Returns a `Facebook\FacebookResponse` object
  $response = $fb->post('/me/feed', $linkData, $accessToken);
} catch(Facebook\Exceptions\FacebookResponseException $e) {
  echo 'Graph returned an error: ' . $e->getMessage();
  exit;
} catch(Facebook\Exceptions\FacebookSDKException $e) {
  echo 'Facebook SDK returned an error: ' . $e->getMessage();
  exit;
}

$graphNode = $response->getGraphNode();

echo 'Posted with id: ' . $graphNode['id'];

?>

I am getting this error "Facebook SDK returned an error: You must provide an access token." I have tried to search around and I haven't got any reliable answers. Anyone who has an idea can share.

来源：https://stackoverflow.com/questions/45862794/facebook-sdk-returned-an-error-you-must-provide-an-access-token-php-facebook-a