title: iOS 8 share extension and authentication flows
body: <p>I have an iOS 8 share extension for posting content from a web browser. Users need to be prompted to login if they've never logged in via the containing app.</p>
  
  <p>Pinterest appears to support fast-switching to the containing app (I'm assuming they've implemented a share extension).</p>
  
  <p>iOS documentation suggests that only Today extensions can <a href="https://developer.apple.com/library/ios/documentation/General/Conceptual/ExtensibilityPG/NotificationCenter.html#//apple_ref/doc/uid/TP40014214-CH11-SW13">open containing apps</a>.</p>
  
  <p>Is there a way to fast-switch to the containing app via a share extension for authentication?</p>