title: Missing OAuth request token cookie error using tornado and TwitterMixin
body: <p>I'm using tornado and the TwitterMixin and I use the following basic code:</p>
  
  <pre><code>class OauthTwitterHandler(BaseHandler, tornado.auth.TwitterMixin): 
      @tornado.web.asynchronous 
      def get(self): 
          if self.get_argument("oauth_token", None): 
              self.get_authenticated_user(self.async_callback(self._on_auth)) 
              return 
          self.authorize_redirect() 
      def _on_auth(self, user): 
          if not user: 
              raise tornado.web.HTTPError(500, "Twitter auth failed") 
          self.write(user) 
          self.finish() 
  </code></pre>
  
  <p>For me it works very well but sometimes, users of my application get a 500 error which says:
   Missing OAuth request token cookie</p>
  
  <p>I don't know if it comes from the browser or the twitter api callback configuration.
  I've looked through the tornado code and I don't understand why this error 
  appears.</p>