title: openid.ui.mode using rails' openid_authentication plugin
body: <p>I'm using the <a href="https://github.com/rails/open_id_authentication" rel="noreferrer">openid_authentication</a> plugin to login my users with openid.</p>
  
  <p>On some pages (the one designed for mobile apps), I'd like to provide the <code>openid.ui.mode = "popup"</code> option so that the provider would display a lighter version of the login page.</p>
  
  <p>Though, it appears the rack-openid gem (on which openid_authentication relies) filters the parameters provided, not allowing anything else than fields.</p>
  
  <p>So doing the following :</p>
  
  <pre><code>authenticate_with_open_id(nil, {'openid.ui.mode' =&gt; 'popup'}) do |result|
  </code></pre>
  
  <p>Does not work.</p>