$helper = $fb->getRedirectLoginHelper();  
try {  
  $accessToken = $helper->getAccessToken();  
} catch(Facebook\Exceptions\FacebookResponseException $e) {  
  // When Graph returns an error  
  echo 'Graph returned an error: ' . $e->getMessage();  
  exit;  
} catch(Facebook\Exceptions\FacebookSDKException $e) {  
  // When validation fails or other local issues  
  echo 'Facebook SDK returned an error: ' . $e->getMessage();  
  exit;  
}
$_SESSION['fb_access_token'] = (string) $accessToken; 
 
try {
  $response = $fb->get('/me',$_SESSION['fb_access_token'],['fields' => 'email']
);
  $userNode = $response->getGraphUser();
} catch(Facebook\Exceptions\FacebookResponseException $e) {
  // When Graph returns an error
  echo 'Graph returned an error: ' . $e->getMessage();
  exit;
} catch(Facebook\Exceptions\FacebookSDKException $e) {
  // When validation fails or other local issues
  echo 'Facebook SDK returned an error: ' . $e->getMessage();
  exit;
}
print_r($userNode);