title: Query OneSignal server from device to get info about push notifications received while app was closed
body: <p>I'm using OneSignal Swift in a native iOS application. So far i'm able to handle all kinds of push notification cases (foreground/background) except one. When user has force closed the application from "task bar switcher". </p>
  
  <p>I'm using <code>'content-available':'true'</code> in all my notifications through OneSignal in order to wake up my app and start running code the exact moment the notification is received. So far so good everything is working as expected. 
  When the app is closed and push notification arrives, if user taps it, then handling with OneSignal works with OSHandleNotificationActionBlock callback. </p>
  
  <p>The problem though is <strong>if user doesn't tap and just opens through application icon, then notification data are completely lost</strong>. <strong>Online reference dictates that the correct way of handling this (what most apps like Facebook do), is query tour APNS (OneSignal in my case) for unhandled notifications and re-fetch them on application start</strong>. So the question is how to do that from OneSignal iOS native SDK? Is it possible? There is ofc the REST Service -which might be the case- but users are clearly discouraged to call the API from inside client application. An app key is necessary which shouldn't be saved in device's keychain apparently for security reasons(??)...</p>