title: Google's OAuth2 login_hint parameter does not work with the sub identifier despite what the docs say?
body: <p>I'm setting login_hint to a previously retrieved sub identifier (unique Google ID) as part of an authorization request url, but it doesn't select the appropriate account. It does do it if instead of the sub I supply the email address of that user.</p>
  
  <p>According to Google's documentation however the sub identifier should also work:</p>
  
  <blockquote>
    <p>Optional. If your application knows which user is trying to
    authenticate, it can use this parameter to provide a hint to the
    Google Authentication Server. The server uses the hint to simplify the
    login flow either by prefilling the email field in the sign-in form or
    by selecting the appropriate multi-login session.</p>
    
    <p>Set the parameter value to an email address or sub identifier, which
    is equivalent to the user's Google ID.</p>
  </blockquote>
  
  <p>Any ideas how to get it working, or whether this is indeed a bug?</p>