code: function validateAuthData(authData, config) {
    var appSecretProof = crypto.createHmac('sha256', config.appSecret).update(authData.access_token).digest('hex');
    return graphRequest('me/?access_token=' + authData.access_token + '&appsecret_proof=' + appSecretProof)
      .then((data) => {
        if (data && data.id == authData.id) {
          return;
        }
        throw new Parse.Error(
          Parse.Error.OBJECT_NOT_FOUND,
          'AccountKit auth is invalid for this user.');
      });
  }
docs: Returns a promise that fulfills iff this user id is valid.