title: iOS Push Notifications - device token management
body: <p>I am adding Push Notifications to my app and I know I need to store the device tokens in my database so that I can send push notifications to specific devices (or all devices). </p>
  
  <p>My question is what is the best practice for maintenance of these device tokens? I can store all device tokens as they are received, but how can I detect and remove old device tokens that are no longer valid? I assume a device token can become invalid if user deletes the app, or if user turns off notifications for the app.</p>
  
  <p>Update - Having a user authentication and linking it to the device token (and updating based on login/logout) makes sense. But what about if the user deletes the app? there is no logout, how do you remove the device token then?</p>