Rate Limiting Logins

Part of the Auth and Security section of Coddy's Node.js journey. Lesson 16 of 17.

A script can try thousands of passwords a minute against one account. Count the failed logins per username, and after five in a minute refuse to check any more until the minute is over.

Status 429 Too Many Requests says why, and the Retry-After header says how many seconds to wait. Count failures only: a person who types the right password must never lock themselves out. A Map in memory is enough for one server; it empties when the server restarts.

const lastSent = new Map();

app.post('/reset', (req, res) => {
    const email = String(req.body.email ?? '').toLowerCase();
    const wait = (lastSent.get(email) ?? 0) + 60_000 - Date.now();
    if (wait > 0) {
        res.set('Retry-After', String(Math.ceil(wait / 1000)));
        return res.status(429).json({ error: 'One reset email a minute' });
    }
    lastSent.set(email, Date.now());
    // ... send the email
});

Challenge

Easy

After 5 failed logins for one username within a minute, POST /login answers 429 { error } for that name, even with the right password.
The 429 has Retry-After: the seconds left in that minute.
Successful logins are never counted.

Try it yourself

import express from 'express';
import { ObjectId } from 'mongodb';
import { randomBytes } from 'node:crypto';
import { parseCookies } from './cookies.js';
import { notes, sessions, users } from './db.js';
import { hashPassword, verifyPassword } from './passwords.js';

const app = express();
app.disable('x-powered-by');
app.use(express.json());

// Headers that tell the browser to be careful with every answer.
app.use((req, res, next) => {
    res.set({
        'X-Content-Type-Options': 'nosniff',
        'Referrer-Policy': 'no-referrer',
        'Content-Security-Policy': "default-src 'self'",
    });
    next();
});

// The one admin account. Its password comes from the environment.
await users.insertOne({ username: 'admin', role: 'admin', passwordHash: await hashPassword(process.env.ADMIN_PASSWORD) });

app.post('/signup', async (req, res) => {
    const username = String(req.body.username ?? '').trim().toLowerCase();
    const password = String(req.body.password ?? '');
    if (!username || password.length < 8) {
        return res.status(400).json({ error: 'Pick a username and a password of at least 8 characters' });
    }
    if (await users.findOne({ username })) {
        return res.status(409).json({ error: 'That username is taken' });
    }
    await users.insertOne({ username, role: 'member', passwordHash: await hashPassword(password) });
    res.status(201).json({ username });
});

app.post('/login', async (req, res) => {
    const username = String(req.body.username ?? '').trim().toLowerCase();
    const user = await users.findOne({ username });
    if (!user || !(await verifyPassword(String(req.body.password ?? ''), user.passwordHash))) {
        return res.status(401).json({ error: 'Wrong username or password' });
    }
    const sid = randomBytes(24).toString('base64url');
    await sessions.insertOne({ _id: sid, userId: user._id, createdAt: new Date() });
    res.cookie('sid', sid, {
        httpOnly: true,
        sameSite: 'lax',
        secure: true,
        maxAge: 24 * 60 * 60 * 1000,
    });
    res.json({ username: user.username });
});

// Finds the user of the session cookie, or answers 401.
async function requireUser(req, res, next) {
    const { sid } = parseCookies(req.get('cookie'));
    const session = sid && (await sessions.findOne({ _id: sid }));
    const user = session && (await users.findOne({ _id: session.userId }));
    if (!user) {
        return res.status(401).json({ error: 'Log in first' });
    }
    req.user = { id: user._id.toHexString(), username: user.username, role: user.role };
    next();
}

// Answers 403 unless the logged in user has this role.
function requireRole(role) {
    return (req, res, next) => {
        if (req.user.role !== role) {
            return res.status(403).json({ error: 'Not allowed' });
        }
        next();
    };
}

app.get('/me', requireUser, (req, res) => {
    res.json({ username: req.user.username });
});

app.post('/logout', async (req, res) => {
    const { sid } = parseCookies(req.get('cookie'));
    if (sid) {
        await sessions.deleteOne({ _id: sid });
    }
    res.clearCookie('sid');
    res.status(204).end();
});

// Your notes as a page.
app.get('/', requireUser, async (req, res) => {
    const list = await notes.find({ owner: req.user.id }).toArray();
    const items = list.map((note) => `<li>${note.text}</li>`).join('');
    res.send(`<!doctype html><title>Vault</title><h1>${req.user.username}'s notes</h1><ul>${items}</ul>`);
});

// Notes: each user reads and writes only their own.
app.get('/notes', requireUser, async (req, res) => {
    res.json(await notes.find({ owner: req.user.id }).toArray());
});

app.post('/notes', requireUser, async (req, res) => {
    const note = { owner: req.user.id, text: String(req.body.text ?? '') };
    await notes.insertOne(note);
    res.status(201).json(note);
});

app.get('/notes/:id', requireUser, async (req, res) => {
    if (!ObjectId.isValid(req.params.id)) {
        return res.status(404).json({ error: 'Note not found' });
    }
    const note = await notes.findOne({ _id: new ObjectId(req.params.id), owner: req.user.id });
    if (!note) {
        return res.status(404).json({ error: 'Note not found' });
    }
    res.json(note);
});

app.delete('/notes/:id', requireUser, async (req, res) => {
    if (!ObjectId.isValid(req.params.id)) {
        return res.status(404).json({ error: 'Note not found' });
    }
    const { deletedCount } = await notes.deleteOne({ _id: new ObjectId(req.params.id), owner: req.user.id });
    if (!deletedCount) {
        return res.status(404).json({ error: 'Note not found' });
    }
    res.status(204).end();
});

// For admins: how many accounts there are.
app.get('/admin', requireUser, requireRole('admin'), async (req, res) => {
    res.json({ users: await users.countDocuments() });
});

app.listen(3000, () => {
    console.log('Vault is running on port 3000');
});