AccessTokenRefreshError: Google Spreadsheet API with oAuth 2.0 Service Account of App Engine App

Question

I\'m trying to access a Google Spreadsheet via the GData API using oAuth 2.0 service-account credentials created for a Python 2.7 app hosted on Google App Engine.

Answer 1

I've figured out that calling SignedJwtAssertionCredentials with-out the sub parameter (for the "impersonated" user) will not produce AccessTokenRefreshError: access_denied

import os
import httplib2
from google.appengine.api import memcache
from apiclient.discovery import build
from oauth2client.client import SignedJwtAssertionCredentials
import gdata.spreadsheets.client
import gdata.spreadsheet.service

# AppAssertionCredentials is not supported in gdata python client library,
# so we use SignedJwtAssertionCredentials with the credential 
# file of this service account.
# Load the key in PKCS 12 format that you downloaded from the Google API
# Console when you created your Service account.
clientEmail = '10346........-g3dp......................3m1em8@developer.gserviceaccount.com'
p12File = 'app.p12'
path = os.path.join(ROOT_DIR, 'data', 'oAuth2', p12File)
impersonateUser = 'user@mygoogleappsdomain.com'
spreadsheetKey = '1mcJHJ...................................juQMw' # ID copied from URL of desired spreadsheet in Google Drive
with open(path) as f:
    privateKey = f.read()
    f.close()

# Getting credentials with AppAssertionCredentials only worked successfully
# for Google API Client Library for Python, e.g. accessing file's meta-data.
# So we use SignedJwtAssertionCredentials, as suggested in
# http://stackoverflow.com/questions/16026286/using-oauth2-with-service-account-on-gdata-in-python
# but with-out the sub parameter!
credentials = SignedJwtAssertionCredentials(
    clientEmail,
    privateKey,
    scope=(
        'https://www.googleapis.com/auth/drive.file ',
        # added the scope above as suggested somewhere else,
        # but error occurs with and with-out this scope
        'https://www.googleapis.com/auth/drive',
        'https://spreadsheets.google.com/feeds',
        'https://docs.google.com/feeds'
    ),
#    sub=impersonateUser
)

http = httplib2.Http()
http = credentials.authorize(http)
auth2token = gdata.gauth.OAuth2TokenFromCredentials(credentials)
# this pattern would eventually also work using SpreadsheetsService()
# SpreadsheetsService methods are different from SpreadsheetsClient, though
#srv = gdata.spreadsheet.service.SpreadsheetsService()
#srv = auth2token.authorize(srv)

clt = gdata.spreadsheets.client.SpreadsheetsClient()
clt = auth2token.authorize(clt)

wks = clt.get_worksheets(spreadsheetKey)
# works now!