Facebook Graph API, how to get users email?

// Facebook SDK v5 for PHP
// https://developers.facebook.com/docs/php/gettingstarted/5.0.0

$fb = new Facebook\Facebook([
  'app_id' => '{app-id}',
  'app_secret' => '{app-secret}',
  'default_graph_version' => 'v2.4',
]);

$fb->setDefaultAccessToken($_SESSION['facebook_access_token']);
$response = $fb->get('/me?locale=en_US&fields=name,email');
$userNode = $response->getGraphUser();
var_dump(
    $userNode->getField('email'), $userNode['email']
);

The only way to get the users e-mail address is to request extended permissions on the email field. The user must allow you to see this and you cannot get the e-mail addresses of the user's friends.

http://developers.facebook.com/docs/authentication/permissions

You can do this if you are using Facebook connect by passing scope=email in the get string of your call to the Auth Dialog.

I'd recommend using an SDK instead of file_get_contents as it makes it far easier to perform the Oauth authentication.