npm install google-auth-library
npm install googleapis

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

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/...');

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)

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);

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

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();
const userId = payload['sub'];
const email = payload['email'];
const name = payload['name'];
const picture = payload['picture'];

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

request = requests.Request()

payload = id_token.verify_oauth2_token(
    token,
    request,
    WEB_CLIENT_ID
)
user_id = payload['sub']
email = payload['email']
name = payload.get('name', '')
picture = payload.get('picture')

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);

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']
)

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' }
});

from googleapiclient.discovery import build

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

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

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