Get google auth tokens from json

auth.py

# python auth.py /path/to/creds.json
# To install
# brew install python
# gcloud components install app-engine-python
# pip install --upgrade google-api-python-client

import sys
import json
import httplib2
import os
from oauth2client.service_account import ServiceAccountCredentials

if sys.argv < 2:
    print "Usage auth [path-to-json]"
else:
    keyPath = sys.argv[1]
    print "Using key from path " + keyPath
    if not os.path.exists(keyPath):
        print "Invalid path"
    else:
        jsonFile = open(keyPath, "r")
        keyJson = json.load(jsonFile)

        creds=ServiceAccountCredentials.from_json_keyfile_dict(keyJson, 'email')
        http=httplib2.Http()
        creds.refresh(http)
        print creds.access_token