Firebase Auth verify JWT ID Tokens without SDK with NodeJS

Question

Using NodeJS, how can I verify the JWT (idToken) provided by Firebase Auth, without Firebase Admin SDK?

Answer 1

Following the doc on how to verify ID Tokens, it is possible using any JWT libraries and grabbing the public key from Google API's website.

import jwt from 'jsonwebtoken';
import request from 'request';
import { promisify } from 'util';
const rp = promisify(request);

const response = await rp('https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com');
const publicKeys = JSON.parse(response.body);

const verifyIdToken = idToken => {
    const header64 = idToken.split('.')[0];
    const header = JSON.parse(Buffer.from(header64, 'base64').toString('ascii'));
    return jwt.verify(token, publicKeys[header.kid], { algorithms: ['RS256'] });
};