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A tiny utility to authenticate requests using GCP OAuth and send CORS headers in Flask

Project description

A small class that helps with authentication and CORS for HTTP-triggered cloud functions written in Python and hosted on GCP

Please note: This is not an officially supported Google product.

If you are using OAuth to authenticate to a Cloud Function written in Python and hosted on GCP, and your client is running in a browser, this is for you. If not, you probably won't find this useful.

This class does three things:

  • Responds correctly and configurably to the HTTP OPTIONS method used by browsers to do pre-flight checks as part of CORS
  • Retrieves an OAuth2 token supplied in the Authorization HTTP header, validates it, and then fetches the information encoded by the token
  • Gives you back either a valid token, or a response to send back to the user in case a valid token can't be found


You can install the latest version of this package using pip:

python3 -m pip install --user gcloud-flask-oauth-cors

It's hosted on pypi:


If you don't have one, create an OAuth client ID and pass it as an environment variable to your cloud function. Then, you can use the following:

import gcloud_flask_oauth_cors as oauth

def my_function_name(request):
    auth = oauth.Auth(os.getenv("OAUTH_CLIENT_ID"))
    id_info = auth.get_id_info(request)
    if id_info is None:
        # If we were called with the HTTP OPTIONS method, this will return the relevant CORS headers.
        # If another HTTP method was used and we can't authenticate, this will return a 401 (Unauthorized)
        return auth.get_response()

    # Do something with the id_info, for example:

On the client side, you can use Google Sign-in. Make sure you pass your id_token in any requests like this:

let xhr = new XMLHttpRequest();
xhr.setRequestHeader("Authorization", "Bearer " + id_token);

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