title: Switching Google accounts for iOS login integration
body: <p><a href="https://developers.google.com/identity/sign-in/ios/" rel="nofollow">Google's login integration guide for iOS</a> does not actually describe the possibility of programmatically switching accounts. </p>
  
  <p>My requirement is to allow the user to switch their Google account, but if they choose to cancel the switch then they should stay logged in with their current credentials. Youtube already do this but I can see they're using a custom built screen instead of the default account selection screen. 
  What I've done so far is to call this when user taps account image</p>
  
  <pre><code>    GIDSignIn.sharedInstance().signOut()
      GIDSignIn.sharedInstance().signIn()
  </code></pre>
  
  <p>which prompts the account selection screen each time, with the disadvantage that, of course, if the user cancels, they will be signed out of the app. There must be a way to preserve the authorisation token in the Keychain, but I don't know they key for it in order to trigger the save before displaying the screen. Is there an easier way to go about this?</p>