Example code of Node.JS based BFF for article: https://medium.com/@gelencser.szabolcs.94/secure-jwts-with-backend-for-frontend-9b7611ad2afb?sk=9287fffc2d60e70088e9b136ec0e25f0

bff_example.js

// MIT License

// Copyright (c) 2020 Szabolcs Gelencsér

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

const express = require('express');
const next = require('next');
const bodyParser = require('body-parser');
const cookieParser = require('cookie-parser');
const fetch = require('isomorphic-unfetch');

const { NODE_ENV, API_URL, PORT } = process.env;

const rtCookieName = 'refreshToken';

const catchErrors = (fn) => async (req, res) => {
	try {
		await fn(req, res);
	} catch (e) {
		console.log(new Date(Date.now()).toISOString(), e);
		res.status(500);
		res.send(e);
	}
};

const fetchAPI = async (path, body, headers) => {
	const res = await fetch(`${API_URL}/api/v1/${path}`, {
		method: 'post',
		headers: {
			'content-type': 'application/json',
			...headers,
		},
		body: JSON.stringify(body),
	});
	return {
		body: await res.text(),
		status: res.status,
		headers: res.headers,
	};
};

const forwardHeader = (res, apiRes, header) => {
	if (apiRes.headers.get(header)) {
		res.set(header, apiRes.headers.get(header));
	}
};

const forwardResponse = (res, apiRes) => {
	forwardHeader(res, apiRes, 'content-type');
	forwardHeader(res, apiRes, 'www-authenticate');
	// additional whitelisted headers here
	res.status(apiRes.status);
	res.send(apiRes.body);
};

const writeRefreshCookie = (res, refreshToken, refreshAge) => {
	res.cookie(rtCookieName, refreshToken, {
		path: '/api/v1/token',
		// received in second, must be passed in as nanosecond
		expires: new Date(Date.now() + refreshAge * 1000 * 1000).toUTCString(),
		maxAge: refreshAge * 1000, // received in second, must be passed in as millisecond
		httpOnly: true,
		secure: NODE_ENV !== 'dev',
		sameSite: 'Strict',
	});
};

const forwardRefreshToken = (res, apiRes) => {
	try {
		const { refreshToken, refreshAge } = JSON.parse(apiRes.body);
		writeRefreshCookie(res, refreshToken, refreshAge);
	} catch { }
};

const nextApp = next({ dev: NODE_ENV === 'dev' });
nextApp.prepare().then(() => {
	const server = express();

	server.use(bodyParser.urlencoded({ extended: true }));
	server.use(bodyParser.json());
	server.use(cookieParser());

	server.post('/api/v1/login', catchErrors(async (req, res) => {
		const apiRes = await fetchAPI('login', req.body);
		forwardRefreshToken(res, apiRes);
		forwardResponse(res, apiRes);
	}));

	server.post('/api/v1/token/refresh', catchErrors(async (req, res) => {
		const refreshToken = req.cookies[rtCookieName];
		const apiRes = await fetchAPI('token/refresh', { refreshToken });
		forwardRefreshToken(res, apiRes);
		forwardResponse(res, apiRes);
	}));

	server.post('/api/v1/token/invalidate', catchErrors(async (req, res) => {
		const refreshToken = req.cookies[rtCookieName];
		const apiRes = await fetchAPI('token/invalidate', { refreshToken });
		writeRefreshCookie(res, '', -1);
		forwardResponse(res, apiRes);
	}));

	server.post('/api/v1/graphql', catchErrors(async (req, res) => {
		const apiRes = await fetchAPI('graphql', req.body, {
			Authorization: req.header('Authorization'),
		});
		forwardResponse(res, apiRes);
	}));

	server.all('*', nextApp.getRequestHandler());

	server.listen(PORT, (err) => {
		if (err) {
			throw err;
		}
		console.log(`> Ready on port ${PORT}`);
	});
})
	.catch((err) => {
		console.log('An error occurred, unable to start the server');
		console.log(err);
	});

Thanks! :) It's in the client repository like this:

server.js (bff_example.js here)
src/
    components/...
    pages/...

Next.js API routes would have worked as well I guess (didn't know them when this solution was implemented).
My only concern about Next.js API routes now is building the Next.js app once and re-using it among different environments (I've written about it in this post).

Thank you for your reply ;) @h3yduck

Hey, i haven't understood, where do you store a refresh token on Auth service?

Hey, I stored it in a DB with a TTL: https://stackoverflow.com/questions/59511628/is-it-secure-to-store-a-refresh-token-in-the-database-to-issue-new-access-toke/59511813#59511813

Hey, I stored it in a DB with a TTL: https://stackoverflow.com/questions/59511628/is-it-secure-to-store-a-refresh-token-in-the-database-to-issue-new-access-toke/59511813#59511813

thank you !

Hey, I am trying to implement this pattern in a React app but I'm finding it difficult to create a sever like this in same domain as my react app. Can you give me an example of how to implement this pattern in React?

hey @SpecterHunt 👋 this pattern must be implemented on the server side (and React is a client-side framework).

The example server hosts a React app as well with Next.js, but the code itself (doing the proxying) runs on the server side.

hey @SpecterHunt 👋 this pattern must be implemented on the server side (and React is a client-side framework).

The example server hosts a React app as well with Next.js, but the code itself (doing the proxying) runs on the server side.

Hi @szabolcsgelencser thank you for the reply. What I meant to ask was, to implement this pattern does your proxy server and client resides in same domain/subdomain?(because of HttpOnly and same site cookies)

Ah, I see, sorry I misunderstood 🙂

Yes they do, I solved it by hosting the React app from the proxy as well (but you can solve it several different ways based on your hosting environment - eg. Kubernetes Ingress also supports routing to various services based on HTTP path prefix having the same domain).

Thank you. Now I have understood the implementation. @szabolcsgelencser I have few more things to ask. Can we connect on LinkedIn?
I've requested you for the connection at LinkedIn. My profile is named Ayush Tripathi.