code: function _loginFacebook(customOptions, successCallback, errorCallback) {
      var options = {scope: 'email'},
        $this = this;
  
      // If there are no facebook custom options, callbacks can start in first param.
      if(Utils.isFunction(customOptions) || customOptions === null){
  
        var tmp = successCallback;
        successCallback = customOptions;
        errorCallback = tmp;
  
      }else if(Utils.isObject(customOptions)){
  
        // If there are custom FB options, use this instead of the defaults.
        options = customOptions;
  
      }
  
      // Return promise and resolve only once authenticated with EVRYTHNG.
      return new Promise(function(resolve, reject) {
  
        // Login using Facebook with options above.
        Facebook.login(options).then(function (userResponse) {
  
          // If successful, authenticate with Evrythng, apply *successCb* and resolve
          // promise. Our own *Facebook.login()* method (defined in the [`social/facebook`
          // module](social/facebook.html)) already resolves with the user information.
          // In this case, we add Evrythng access data to this already wrapped response.
          authFacebook.call($this, userResponse).then(function (fullResponse) {
  
            if (successCallback) {
              Logger.warnCallbackDeprecation();
              successCallback(fullResponse);
            }
            resolve(fullResponse);
  
          });
  
        }, function (response) {
  
          // Login was not successful, apply *errorCb* and reject promise. Response
          // has Facebook's *authResponse* and *status* objects.
          if (errorCallback) {
            Logger.warnCallbackDeprecation();
            errorCallback(response);
          }
          reject(response);
  
        });
  
      });
    }
docs: **Default Facebook scope permission is simply *'email'*. If your application needs more than that, please read about Facebook login options and permissions on their [Developer Docs](https://developers.facebook.com/docs/reference/javascript/FB.login/v2.0)**.