text: from typing import Tuple
  from oauthenticator.generic import GenericOAuthenticator
  
  from tornado.httpclient import HTTPRequest, AsyncHTTPClient
  
  from jupyterhub.handlers.base import BaseHandler
  
  # add route for terms & conditions
  class TermsConditionsHandler(BaseHandler):
  
      def get(self): # pylint: disable=arguments-differ
          """Terms and conditions"""
          # Note: This placeholder serves a demonstration for adding
          # additional routes and associated handlers.
          self.write("This is the terms and conditions of this service.")
      
  class MarketplaceOAuthenticator(GenericOAuthenticator):
      """A GenericOAuthenticator with assigned LoginHandler containing Marketplace specific urls"""
  
      async def _fetch_user_details(self, access_token):
          """Get user details from Marketplace user-service API from user ID"""
          import json
  
          http_client = AsyncHTTPClient()
          headers = {
              "Accept": "application/json",
              "User-Agent": "JupyterHub",
              "Authorization": f"Bearer {access_token}",
          }
  
          # Use GET request method
          req = HTTPRequest(
              "https://{{ marketplace_host }}/user-service/userinfo",
              method="GET",
              headers=headers,
              validate_cert=False,
          )
          resp = await http_client.fetch(req)
          resp_json = json.loads(resp.body.decode('utf8', 'replace'))
  
          return resp_json
  
      async def authenticate(self, handler, data=None):
          """Overloads authentication service to include an additional call to marketplace user-service API."""
          resp_json = await super().authenticate(handler, data=data)
  
          # Get full user details
          access_token = resp_json['auth_state']['access_token']
          user_json = await self._fetch_user_details(access_token)
  
          # Update real username and store additional details in in auth_state
          resp_json['name'] = user_json['name']
          resp_json['auth_state']['oauth_user'].update(user_json)
  
          return resp_json
  
      async def pre_spawn_start(self, user, spawner):
          """Pass upstream_token to spawner via environment variable"""
          auth_state = await user.get_auth_state()
          if not auth_state:
              # auth_state not enabled
              return
          spawner.environment['MP_HOST'] = "https://{{ marketplace_host }}"
          spawner.environment['MP_ACCESS_TOKEN'] = auth_state['access_token']
          spawner.environment['MP_REFRESH_TOKEN'] = auth_state['refresh_token']
  