Cloud Functions上でのHTTPリクエストをする際の認証方法について

前提・実現したいこと

Google Cloud FunctionsからGoogle App Scriptへwebhookを渡すコードを書いています。
現在HTTPリクエスト処理で認証に失敗し、401エラーが出ている状態です。

発生している問題・エラーメッセージ

urllib.error.HTTPError: HTTP Error 401: Unauthorized
at http_error_default (/opt/python3.9/lib/python3.9/urllib/request.py:641)
at _call_chain (/opt/python3.9/lib/python3.9/urllib/request.py:494)
at error (/opt/python3.9/lib/python3.9/urllib/request.py:561)
at http_response (/opt/python3.9/lib/python3.9/urllib/request.py:632)
at open (/opt/python3.9/lib/python3.9/urllib/request.py:523)
at urlopen (/opt/python3.9/lib/python3.9/urllib/request.py:214)
at handler (/workspace/main.py:19)
at view_func (/layers/google.python.pip/pip/lib/python3.9/site-packages/functions_framework/__init__.py:80)
at dispatch_request (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/app.py:1936)
at full_dispatch_request (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/app.py:1950)
at reraise (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/_compat.py:39)
at handle_user_exception (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/app.py:1821)
at full_dispatch_request (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/app.py:1952)
at wsgi_app (/layers/google.python.pip/pip/lib/python3.9/site-packages/flask/app.py:2447)

該当のソースコード

main.py

python
1import urllib.request, json
2import google.auth.transport.requests
3import requests
4import google.oauth2.id_token
5
6def handler(req):
7	print(req);
8	url = "https://script.google.com/macros/s/XXXXXXXXXXXXXXXX/exec" # エンドポイント
9	
10	auth_req = google.auth.transport.requests.Request()
11	id_token = google.oauth2.id_token.fetch_id_token(auth_req, url)
12	token = "Bearer "+id_token
13
14	headers = {"Content-Type": "application/json; charset=utf-8" , "Authorization": token}
15	request_json = req.get_json()
16
17	request = urllib.request.Request(url, json.dumps(request_json).encode(), header=headers, method="POST")
18
19	with urllib.request.urlopen(request) as response:
20		response_body = response.read().decode("utf-8")
21	
22	result = {"statusCode": 200, "body": response_body, "headers": headers }
23	
24	return result
25