Howto write a python-based firebase https function?

The answer by Kelvin pointed me in the right direction. However the python code (as a minimal working example) could look like this:

from flask import jsonify
import firebase_admin
from firebase_admin import auth

# Initialize the app without credentials, as the function gets it from context
firebase_admin.initialize_app()


def verifyRequest(request):
    authorization = request.headers.get('Authorization')
    token = authorization.split('Bearer ')[1]
    try:
        # This will fail in every situation BUT successful authentication
        decode_token = auth.verify_id_token(id_token=token)
    except Exception as e:
        print('Authorization failed')
        print(e)
        return jsonify({
        'data': {
            'status': 'Authorization failed'
        }})

    print('Authorization suceeded')
    return jsonify({
        'data': {
            'status': 'Authorization succeeded'
        }})

note that the function auth.verify_id_token() will raise an error when the authentication failed.

you can upload this via gcloud an the following command:

gcloud functions deploy verifyRequest --runtime python37 --trigger-http --project <YourProjectID>