code: def login_handler(self, config=None, prefix=None, **args):
          
          params = {
              'response_type': 'code',
              'client_id': self.google_api_client_id,
              'redirect_uri': self.scheme_host_port_prefix(
                  'http', config.host, config.port, prefix) + '/home',
              'scope': self.google_api_scope,
              'state': self.request_args_get('next', default=''),
          }
          url = self.google_oauth2_url + 'auth?' + urlencode(params)
          return self.login_handler_redirect(url)
docs: OAuth starts here, redirect user to Google.