Use Application Default Credentials on Google Comp

Question

Does the ADC (Application Default Credentials) workflow only support Google Cloud APIs (for example, supports for Google Cloud Storage API, but not the Google Sheet API)?

I'm referring to google.auth's default method - not having to store any private keys with the code is a great win and the main benefit of making effective use of the ADC (Application Default Credentials) setup.

The following code works if I set the GOOGLE_APPLICATION_CREDENTIALS environmental variable to the private key file, say key.json. This is inline with the default method as per step 1 of the google.auth package: 1. If the environment variable GOOGLE_APPLICATION_CREDENTIALS is set to the path of a valid service account JSON private key file, then it is loaded and returned.

import google.auth
from apiclient import discovery

credentials, project_id = google.auth.default(scopes=['https://www.googleapis.com/auth/spreadsheets'])

sheets = discovery.build('sheets', 'v4', credentials=credentials)

SPREADSHEETID = '....'

result = sheets.spreadsheets().values().get(spreadsheetId=SPREADSHEETID, range='Sheet1!A:B').execute()

print result.get('values', [])

Now, looking at step 4 of the method: 4. If the application is running in Compute Engine or the App Engine flexible environment then the credentials and project ID are obtained from the Metadata Service.

If i remove the GOOGLE_APPLICATION_CREDENTIALS environmental variable on a Google Compute instance, I get the following error:

googleapiclient.errors.HttpError: <HttpError 403 when requesting https://sheets.googleapis.com/v4/spreadsheets/..../values/Sheet1%21A%3AB?alt=json returned "Request had insufficient authentication scopes.">

This is not consistent with Google's wizard as per the Cloud Console:

Answer 1

According to this documentation, the scope that you're using requires Oauth 2.0 authorization. Therefore, a user login and consent is required.