title: Use Parse.com to send push to specific user
body: <p>This question is more about security issue.</p>
  
  <p>In order to send push notification to a specific user, I have that user subscribe to his/her own userID. The reason is that I do not need to know all the device tokens for this user, and I can just send the notification to channel "userID", and be certain that all subscribed devices will be notified. However, because anyone can subscribe to any channel, and userID is not that secret. So I wonder if there is a better way to target specific user (by userID) with Parse?</p>