title: How to programatically stop a ReplayKit 2 system broadcast without RPSystemBroadcastPickerView
body: <p>I am trying to implement a broadcast upload extension and I want the user to be able to click a button in my app to stop the broadcast.</p>
  <p>As far as I can tell from the docs, the only ways to stop a system broadcast are:</p>
  <ul>
  <li>Show <code>RPSystemBroadcastPickerView</code> in the app, when the user clicks it, they are taken to the system UI and stop the broadcast there.</li>
  <li>Signal the broadcast extension to stop via other means and call <code>finishBroadcastWithError</code> in <code>RPBroadcastSampleHandler</code> which will show the user an error popup. It's a trick that Zoom seems to use.</li>
  </ul>
  <p>However, I was trying the screen sharing feature on Facebook Messenger today and they are somehow bypassing the system UI (to stop the stream only).
  When I click the stop button, the screen sharing stops immediately and doesn't show either the system UI or the error popup</p>
  <p>How are they doing this?
  My best guess is that they somehow get a valid <code>RPBroadcastController</code> object but I can't figure out how.</p>