Google Auth

Google Authentication for Node.js & Python

Libraries

Node.js

• google-auth-library — core auth library (OAuth2Client, GoogleAuth, JWT, Compute, Impersonated)
• googleapis — Google API client (wraps google-auth-library)

npm install google-auth-library
npm install googleapis

The client.fetch() calls below require google-auth-library ≥ 10.1.0 (the fetch-compatible API landed in 10.1.0, 2025-06-12); on 9.x use client.request() with the same arguments. Checked 2026-08-31: latest is 11.x and keeps both methods.

Python

• google-auth — core auth library (google.oauth2, google.auth, credentials, transport)
• google-auth-oauthlib — OAuth 2.0 user-credential flow helpers (Flow, InstalledAppFlow)
• google-api-python-client — Google API client (wraps google-auth)

pip install google-auth
pip install google-auth-oauthlib
pip install google-api-python-client

Authentication Methods Overview

Quick Patterns

1. Application Default Credentials (ADC)

Node.js

const {GoogleAuth} = require('google-auth-library');

const auth = new GoogleAuth({
  scopes: 'https://www.googleapis.com/auth/cloud-platform'
});
const client = await auth.getClient();
const res = await client.fetch('https://dns.googleapis.com/dns/v1/projects/...');

Python

import google.auth
import google.auth.transport.requests

credentials, project = google.auth.default(
    scopes=['https://www.googleapis.com/auth/cloud-platform']
)
request = google.auth.transport.requests.Request()
credentials.refresh(request)

ADC search order (env var FIRST — this line was reversed): GOOGLE_APPLICATION_CREDENTIALS env var → gcloud auth application-default login file → attached service account (metadata). Print the RESOLVED principal and source (no secret) before configuring — with more than one present, only the resolved source names which you are actually using.

For detailed ADC setup and service account usage, see references/adc-and-service-accounts.md.

2. OAuth 2.0 Web Server Flow

Node.js

const {OAuth2Client} = require('google-auth-library');

const client = new OAuth2Client({
  clientId: CLIENT_ID,
  clientSecret: CLIENT_SECRET,
  redirectUri: REDIRECT_URI
});

const authUrl = client.generateAuthUrl({
  access_type: 'offline',
  scope: ['https://www.googleapis.com/auth/userinfo.profile'],
  state: crypto.randomBytes(32).toString('hex'),
  include_granted_scopes: true
});

// After redirect: exchange code for tokens
const {tokens} = await client.getToken(code);
client.setCredentials(tokens);

Python

from google_auth_oauthlib.flow import Flow

flow = Flow.from_client_secrets_file(
    'client_secret.json',
    scopes=['https://www.googleapis.com/auth/userinfo.profile'],
    redirect_uri=REDIRECT_URI
)

authorization_url, state = flow.authorization_url(
    access_type='offline',
    include_granted_scopes='true'
)

# After redirect: exchange code for tokens
flow.fetch_token(code=code)
credentials = flow.credentials

refresh_token is only returned on the first authorization. Use prompt: 'consent' (Node.js) or prompt='consent' (Python) to force re-consent.

For the complete OAuth 2.0 flow (parameters, token exchange, refresh, revocation, incremental auth), see references/oauth2-web-server.md.

3. Verifying a Google ID Token — the library call

Node.js

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client();

const ticket = await client.verifyIdToken({
  idToken: token,
  audience: WEB_CLIENT_ID,
});
const payload = ticket.getPayload();

Python

from google.oauth2 import id_token
from google.auth.transport import requests

payload = id_token.verify_oauth2_token(token, requests.Request(), WEB_CLIENT_ID)

The call checks signature, aud, exp and iss — and nothing else. That is the library contract, not the web sign-in contract: for the sign-in security checklist (nonce binding, email_verified, login-CSRF defense, account linking) use the google-signin skill — it is the one home for that contract, and this skill deliberately does not restate it.

4. JWT / Service Account

Node.js

const {JWT} = require('google-auth-library');
const keys = require('./service-account-key.json');

const client = new JWT({
  email: keys.client_email,
  key: keys.private_key,
  scopes: ['https://www.googleapis.com/auth/cloud-platform'],
});
const res = await client.fetch(url);

Python

from google.oauth2 import service_account

credentials = service_account.Credentials.from_service_account_file(
    'service-account-key.json',
    scopes=['https://www.googleapis.com/auth/cloud-platform']
)

# Or from a dict already loaded into memory:
credentials = service_account.Credentials.from_service_account_info(
    info,
    scopes=['https://www.googleapis.com/auth/cloud-platform']
)

5. API Key

Node.js

const {OAuth2Client} = require('google-auth-library');
const client = new OAuth2Client({ apiKey: 'my-api-key' });

// Or via GoogleAuth:
const {GoogleAuth} = require('google-auth-library');
const auth = new GoogleAuth({
  clientOptions: { apiKey: 'my-api-key' }
});

Python

from googleapiclient.discovery import build

service = build('customsearch', 'v1', developerKey='my-api-key')

6. Token Refresh

Node.js

client.on('tokens', (tokens) => {
  if (tokens.refresh_token) {
    // Store refresh_token — only sent on first auth
  }
  console.log(tokens.access_token);
});

Python

from google.auth.transport.requests import Request

if credentials.expired and credentials.refresh_token:
    credentials.refresh(Request())
    # credentials.token is the new access token
    # credentials.expiry is the new expiration datetime

Security Best Practices

• Never expose client_secret or service account keys in client-side code
• Always validate state parameter to prevent CSRF in OAuth flows
• Use sub (not email) as the unique user identifier from Google ID tokens
• Store refresh_token securely; it's only returned on first authorization
• Validate external credential configurations before use (check token_url, service_account_impersonation_url point to googleapis.com)
• Prefer Workload Identity Federation over service account keys for non-GCP environments
• For end-user web sign-in, apply the google-signin skill's full checklist — a partial restatement here is how the two skills drifted apart once already
• Fail closed on a missing production secret. The session signing secret, and any credential-store key, is REQUIRED in production with NO dev fallback — a hardcoded default signs every deployment's cookies with a key that lives in the repo. Missing → refuse to boot, never a warning-and-continue (DV-07).
• Logs are sanitized; a credential never reaches one. No token, no client_secret, no refresh_token, no session value in a log line, a stack trace, or an error message — a token in a log is a token anyone with log access holds. Redact by allow-list, not by trying to strip the secret out.
• HTTPS is mandatory and the credential store can fail. The auth cookie is Secure and the callback refuses plain HTTP (an OAuth code over http:// is a code on the wire); and a credential-store read/write that FAILS is an auth failure — re-prompt or 503, never proceed as if the credentials loaded.
• Python-specific: reuse a single google.auth.transport.requests.Request() instance across verifications for connection pooling; do not create a new one per call in hot paths

Reference Files

• OAuth 2.0 Web Server Flow — Complete OAuth 2.0 flow: parameters, consent, token exchange, refresh, revocation, incremental auth, error handling (Node.js + Python)
• ADC & Service Accounts — Application Default Credentials setup, service account keys, JWT, Compute credentials, environment configuration (Node.js + Python)
• Sign In with Google — Google Identity Services (GIS), ID token verification, CSRF protection, One Tap, FedCM (Node.js + Python)
• Workload Identity Federation — AWS, Azure, OIDC/SAML federation, workforce identity, executable-sourced credentials (Node.js + Python)