docs: def doVerify(self):
          """Process the form submission, initating OpenID verification.
          """
  
          # First, make sure that the user entered something
          openid_url = self.query.get('openid_identifier')
          if not openid_url:
              self.render(
                  'Enter an OpenID Identifier to verify.',
                  css_class='error',
                  form_contents=openid_url)
              return
  
          immediate = 'immediate' in self.query
          use_sreg = 'use_sreg' in self.query
          use_pape = 'use_pape' in self.query
          use_stateless = 'use_stateless' in self.query
          oidconsumer = self.getConsumer(stateless=use_stateless)
          try:
              request = oidconsumer.begin(openid_url)
          except consumer.DiscoveryFailure as exc:
              fetch_error_string = 'Error in discovery: %s' % (
                  cgi.escape(str(exc)))
              self.render(
                  fetch_error_string,
                  css_class='error',
                  form_contents=openid_url)
          else:
              if request is None:
                  msg = 'No OpenID services found for <code>%s</code>' % (
                      cgi.escape(openid_url), )
                  self.render(msg, css_class='error', form_contents=openid_url)
              else:
                  # Then, ask the library to begin the authorization.
                  # Here we find out the identity server that will verify the
                  # user's identity, and get a token that allows us to
                  # communicate securely with the identity server.
                  if use_sreg:
                      self.requestRegistrationData(request)
  
                  if use_pape:
                      self.requestPAPEDetails(request)
  
                  trust_root = self.server.base_url
                  return_to = self.buildURL('process')
                  if request.shouldSendRedirect():
                      redirect_url = request.redirectURL(
                          trust_root, return_to, immediate=immediate)
                      self.send_response(302)
                      self.send_header('Location', redirect_url)
                      self.writeUserHeader()
                      self.end_headers()
                  else:
                      form_html = request.htmlMarkup(
                          trust_root,
                          return_to,
                          form_tag_attrs={'id': 'openid_message'},
                          immediate=immediate)
  
                      self.wfile.write(bytes(form_html, 'utf-8'))