[...]
 instance YesodAuth App where
         loginHandler = defaultLayout $ do
             [whamlet|
                 <form method="get" action=@{AuthR forwardUrl} >
                     <input type="hidden" name="openid_identifier" value="https://www.google.com/accounts/o8/id">
                     <button class="btn-openid">
                         <span>Login via Google
            |]
  [...]