server.js

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

dotenv.config();
const client = new OAuth2Client(process.env.REACT_APP_GOOGLE_CLIENT_ID)

const app = express();
app.use(express.json());

const users = [];

function upsert(array, item) {
    const i = array.findIndex((_item) => _item.email === item.email);
    if(i > -1) array[i] = item;
    else array.push(item);
}

app.post('/api/google-login', async ( req, res) => {
    const { token } = req.body;
    const ticket = await client.verifyIdToken({
        idToken: token,
        audience: process.env.CLIENT_ID
    });
    const { name, email, picture} = ticket.getPayload();
    upsert(users, { name, email, picture });
    res.status(201);
    res.json({ name, email, picture })
});

app.use(express.static(path.join(__dirname, '/build')));
app.get('*', (req, res) =>
    res.sendFile(path.join(__dirname, '/build/index.html'))
)
app.listen(process.env.PORT || 5000, () => {
    console.log(`Server is ready at http://localhost:${process.env.PORT || 5000}`)
})