next-csrf

CSRF mitigation for Next.js.

Features

Mitigation patterns that next-csrf implements:

• Synchronizer Token Pattern using csrf (Also read Understanding CSRF)

Installation

With yarn:

yarn add next-csrf

With npm:

npm i next-csrf --save

Usage

Create an initialization file to add options:

// file: lib/csrf.js

import { nextCsrf } from "next-csrf";

const { csrf, setup } = nextCsrf({
    // eslint-disable-next-line no-undef
    secret: process.env.CSRF_SECRET,
});

export { csrf, setup };

Protect an API endpoint:

// file: pages/api/protected.js

import { csrf } from '../lib/csrf';

const handler = (req, res) => {
    return res.status(200).json({ message: "This API route is protected."})
}

export default csrf(handler);

Test the protected API route by sending a POST request from your terminal. Since this request doesn't have the proper token setup, it wil fail.

curl -X POST http://localhost:3000/api/protected
>> {"message": "Invalid CSRF token"}

Use an SSG page to set up the token. Usually, you use CSRF mitigation to harden your requests from authenticated users, if this is the case then you should use the login page.

// file: pages/login.js

import { setup } from '../lib/csrf';

function Login() {
    const loginRequest = async (event) => {
        event.preventDefault();
        
        // The secret and token are sent with the request by default, so no extra
        // configuration is needed in the request.
        const response = await fetch('/api/protected', {
            method: 'post'
        });
        
        if (response.ok) {
            console.log('protected response ok');
        }
    }
    
    return (
        <form onSubmit={loginRequest}>
            <label>
                Username
                <input type="text" required />
            </label>
            
            <label>
                Password
                <input type="password" required />
            </label>
            
            <button>Submit</button>
        </form>
    )
}

// Here's the important part. `setup` saves the necesary secret and token.
export const getServerSideProps = setup(async ({req, res}) => {
    return { props: {}}
});

export default Login;

API

nextCsrf(options);

Returns two functions:

• setup Setups two cookies, one for the secret and other one for the token. Only works on SSG pages.
• csrf Protects API routes from requests without the token. Validates and verify signatures on the cookies.

options

• tokenKey (string) The name of the cookie to store the CSRF token. Default is "XSRF-TOKEN".
• csrfErrorMessage (string) Error message to return for unauthorized requests. Default is "Invalid CSRF token".
• ignoredMethods: (string[]) Methods to ignore, i.e. let pass all requests with these methods. Default is ["GET", "HEAD", "OPTIONS"].
• cookieOptions: Same options as https://www.npmjs.com/package/cookie