Google Service Account Impersonation

adc.py

import googleapiclient.errors
import requests
from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build

def GetCredentials(client_id, client_secret, refresh_token):
    """Convert ADC to access_token/Credential"""
    params = {
            "grant_type": "refresh_token",
            "client_id": client_id,
            "client_secret": client_secret,
            "refresh_token": refresh_token
    }

    authorization_url = "https://www.googleapis.com/oauth2/v4/token"

    r = requests.post(authorization_url, data=params)

    if r.ok:
        credentials = Credentials(token=r.json()['access_token'])
        return credentials
    else:
        return None

imp.py

import googleapiclient.errors
from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
# https://stackoverflow.com/questions/54321848/how-to-use-refresh-token-google-api-in-python ADC Token

def Impersonate(lifetime, targetServiceAccount)
    """Service Account Impersonation"""
    try:
        creds = build('iamcredentials', 'v1', cache_discovery=False).projects().serviceAccounts().generateAccessToken(
        name='projects/-/serviceAccounts/'+targetServiceAccount,
        body = {
            'lifetime': lifetime+'s',
            'scope': ['https://www.googleapis.com/auth/cloud-platform']
        }).execute()
    except googleapiclient.errors.HttpError as e:
        print(e)
        pass
    credentials = Credentials(token=creds['accessToken'])
    return credentials

pubsub.py

#https://markhneedham.com/blog/2015/11/28/python-parsing-a-json-http-chunking-stream/

from google.cloud import pubsub_v1
from google.api_core import exceptions
import os
import requests
import json

topic_name = os.getenv('TOPIC_NAME')
project_id = os.getenv('PROJECT_ID')

def PublishToPubSub(topic_name, payload):
    publisher = pubsub_v1.PublisherClient()
    try:
        publisher.publish(
            topic = 'projects/'+project_id+'/topics/'+topic_name,
            data = payload.encode("utf-8")
        )
    except exceptions.ClientError as e:
        print(e)

dummy_json = requests.get('https://jsonplaceholder.typicode.com/todos/1').json()
PublishToPubSub(topic_name, json.dumps(dummy_json))