Passport.js + Firestore auth config

db.js

require('dotenv').config();
const firebaseAdmin = require('firebase-admin');

firebaseAdmin.initializeApp({
    credential: firebaseAdmin.credential.cert({
      "type": process.env.TYPE,
      "project_id": process.env.PROJECT_ID,
      "private_key_id": process.env.PRIVATE_KEY_ID,
      "private_key": process.env.PRIVATE_KEY.replace(/\\n/g, '\n'),
      "client_email": process.env.CLIENT_EMAIL,
      "client_id": process.env.CLIENT_ID,
      "auth_uri": process.env.AUTH_URI,
      "token_uri": process.env.TOKEN_URI,
      "auth_provider_x509_cert_url": process.env.AUTH_PROVIDER_CERT_URL,
      "client_x509_cert_url": process.env.CLIENT_CERT_URL
    }),
  });

const db = firebaseAdmin.firestore();

module.exports = db;

passport.js

const LocalStrategy = require('passport-local').Strategy;
const bcrypt = require('bcryptjs');
const db = require('../config/db');
const User = db.collection('users');

module.exports = passport => {
    passport.use(
        new LocalStrategy({ usernameField: 'username' }, (username, password, done) => {
            const user = User.doc(username).get()
              .then(user => {
                  bcrypt.compare(password, user.data()['password'], (err, match) => {
                      if (err) throw err;
                      if (!match) { return done(null, false, { message: 'Password does not match.' }); }
                      else { return done(null, user); }
                  });
              })
              .catch(err => {
                  console.log(err);
                  return done(null, false, { message: 'No user found.' });
              });
        })
    );

    passport.serializeUser((user, done) => {
        done(null, user.id);
    });

    passport.deserializeUser((id, done) => {
        const user = User.doc(id).get()
          .then(user => done(null, user))
          .catch(err => done(err, user));
    });
}