How to correctly use facebook scope to get user email?

I need to retrieve a user's email when they use facebook login on my website. Facebook has a scope parameter in their login URL that 开发者_JAVA技巧requests for these extended permissions. What exactly do I add to this code that will properly set scope to include email??

/**
* Get a Login URL for use with redirects. By default, full page redirect is
* assumed. If you are using the generated URL with a window.open() call in
* JavaScript, you can pass in display=popup as part of the $params.
*
* The parameters:
* - redirect_uri: the url to go to after a successful login
* - scope: comma separated list of requested extended perms
*
* @param Array $params provide custom parameters
* @return String the URL for the login flow
*/
public function getLoginUrl($params=array()) {
 $this->establishCSRFTokenState();
 $currentUrl = $this->getCurrentUrl();
 return $this->getUrl(
   'www',
   'dialog/oauth',
   array_merge(array(
                 'client_id' => $this->getAppId(),
                 'redirect_uri' => $currentUrl, // possibly overwritten
                 'state' => $this->state),
               $params));
}

Add the scope parameter:

public function getLoginUrl($params=array()) {
 $this->establishCSRFTokenState();
 $currentUrl = $this->getCurrentUrl();
 return $this->getUrl(
   'www',
   'dialog/oauth',
   array_merge(array(
                 'client_id' => $this->getAppId(),
                 'redirect_uri' => $currentUrl, // possibly overwritten
                 'state' => $this->state,
                 'scope'=>'email'),
               $params));
}