How to implement authentication in Next.js

Question

I am new to Next.js and I am struggling with the authentication system using jwt token. I want to know what is the best / standard way to store the jwt token and routing with the authentication system. I have been trying different approaches, from different tutorials/articles, but do not quite understand it. Here are what I have tried.

1. When the user login, it sends username/password to a separated API server (ex. new project that handles backend stuff), the server will respond with the access-token, then in Next.js project, I set the cookie with that received token. In Next.js project, protected routes will be wrapped with a withAuth hoc, which will check for the token in a cookie. The problem with this approach is that it is vulnerable to XSS because the cookie has no httpOnly flag.

2. This is similar to 1.) but using localStorage, the problem is access-token could not be sent to the server on the first request. (This one I'm not sure, but in my understanding, in every HTTP request, I must stick my access-token manually, so what about requests that I have no control over? ex. first request or using <a> tag).

3. I wrote authentication backend inside Next.js server (custom express server). When the user login, the server will validate it and then set an httpOnly cookie. Then the problem is, with client-side routing (go to URL using Next.js Router), it could not check for token. For example, if a page is wrapped with withAuth hoc, but it cannot access the token inside cookies with javascript.

And I've seen a lot of people, in getInitialProps of the protected route, they only check for existence token in cookie / localStorage, then what if the token is being revoked or blacklisted, how do they handle it because they did not send the token to the server? Or do I have to send the token to the server in every client-side page change?

Answer 1

Since we are on quarantine I have enough time to answer this question. It will be a long answer.

Next.js uses the App component to initialize the pages. _app page is responsible for rendering our pages. We authenticate users on _app.js because anything that we return from getInitialProps can be accessed by all of the other pages. We authenticate user here, authentication decision will be passed to pages, from pages to header, so each page can decide if the user is authenticated or not. (Note that it could be done with redux without prop drilling but it would make the answer more complex)

  static async getInitialProps({ Component, router, ctx }) {
    let pageProps = {};
    const user = process.browser
      ? await auth0.clientAuth()
      : await auth0.serverAuth(ctx.req); // I explain down below

    //this will be sent to all the components
    const auth = { user, isAuthenticated: !!user };
    if (Component.getInitialProps) {
      pageProps = await Component.getInitialProps(ctx);
    }

    return { pageProps, auth };
  }

  render() {
    const { Component, pageProps, auth } = this.props;
    return <Component {...pageProps} auth={auth} />;
  }
}

If we are on the browser and need to check if a user is authenticated, we just retrieve the cookie from the browser, which is easy. But we always have to verify the token. It is the same process used by browser and server. I will explain down below. But if we are on the server. we have no access to the cookies in the browser. But we can read from the "req" object because cookies are attached to the req.header.cookie. this is how we access to cookies on the server.

async serverAuth(req) {
    // console.log(req.headers.cookie) to check
    if (req.headers.cookie) {
      const token = getCookieFromReq(req, "jwt");
      const verifiedToken = await this.verifyToken(token);
      return verifiedToken;
    }
    return undefined;
  }

here is getCookieFromReq(). remember we have to think functional.

const getCookieFromReq = (req, cookieKey) => {
  const cookie = req.headers.cookie
    .split(";")
    .find((c) => c.trim().startsWith(`${cookieKey}=`));

  if (!cookie) return undefined;
  return cookie.split("=")[1];
};

Once we get the cookie, we have to decode it, extract the expiration time to see if it is valid or not. this part is easy. Another thing we have to check is if the signature of the jwt is valid. Symmetric or asymmetric algorithms are used to sign the jwt. You have to use private keys to validate the signature of symmetric algorithms. RS256 is the default asymmetric algorithms for APIs. Servers that use RS256, provide you with a link to get jwt to use the keys to validate the signature. You can either use [jwks-rsa][1] or you can do on your own. You have to create a certificate and then verify if the token is valid.

Assume that our user authenticated now. You said, "And I've seen a lot of people, in getInitialProps of the protected route, they only check for existence token in cookie / localStorage,". We use protected routes to give access only to the authorized users. In order to access those routes, users have to show their jwt tokens and express.js uses middlewares to check if the user's token is valid. Since you have seen a lot of examples, I will skip this part.

"then what if the token is being revoked or blacklisted, how do they handle it because they did not send the token to the server? Or do I have to send the token to a server in every client-side page changing?"

with verifying token process we are 100% sure if the token is valid or not. When a client asks the server to access some secret data, the client has to send the token to the server. Imagine when you mount the component, component asks the server to get some data from the protected routes. The server will extract the req object, take the jwt and use it to fetch data from the protected routes. Implementation of the fetching data for browser and server are different. And if the browser makes a request, it just needs the relative path but the server needs an absolute path. As you should know fetching data is done getInitialProps() of the component and this function executed on both client and server. here is how you should implement it. I just attached the getInitialProps() part.

MyComponent.getInitialProps = async (ctx) => {
  const another = await getSecretData(ctx.req);
 //reuslt of fetching data is passed to component as props
  return { superValue: another };
};



    const getCookieFromReq = (req, cookieKey) => {
      const cookie = req.headers.cookie
        .split(";")
        .find((c) => c.trim().startsWith(`${cookieKey}=`));

      if (!cookie) return undefined;
      return cookie.split("=")[1];
    };

   
    const setAuthHeader = (req) => {
      const token = req ? getCookieFromReq(req, "jwt") : Cookies.getJSON("jwt");

      if (token) {
        return {
          headers: { authorization: `Bearer ${token}` },
        };
      }
      return undefined;
    };

    
    export const getSecretData = async (req) => {
      const url = req ? "http://localhost:3000/api/v1/secret" : "/api/v1/secret";
      return await axios.get(url, setAuthHeader(req)).then((res) => res.data);
    };



  [1]: https://www.npmjs.com/package/jwks-rsa

Answer 2

With the introduction of Next.JS v8, there are examples placed in the NextJS example page. The basic idea to follow is:

JWT

• Using cookies to store the token (you may choose to further encrypt it or not)
• Sending the cookies as authorization headers

OAuth

• Using a third-party authentication service such as OAuth2.0
• Using Passport

Answer 3

This question might need an updated answer, now middlewares are there in Next.js 12 (october 2021): https://nextjs.org/docs/middleware

I am drafting a comprehensive answer to explain auth in Next.js more deeply, you can follow the progress there on GitHub

Here I'll try to propose a summary for Next.js, using middlewares.

Verifying the token after auth and redirecting accordingly

Most of the answer from @Yilmaz from april 2020 is still relevant. However, previously, we had to use getInitialProps in _app to process the request OR a custom server.

This is no longer the case.. Using a middleware let's you achieve a similar purpose, with cleaner code. Because middleware are specifically designed for such use cases.

Here, I suppose you get a JWT access token using an asymetrical algorithm like RS256, exactly like in this previous answer.

Here is a possible implementation:

import { NextFetchEvent, NextRequest, NextResponse } from "next/server";

const removeCookie = (res: NextResponse, cookieName: string) => {
  res.headers.append("Set-Cookie", `${cookieName}=; Max-Age=-1; Path=/`);
  return res;
};

export default async function middleware(
  req: NextRequest,
  ev: NextFetchEvent
) {
  const { pathname } = req.nextUrl;
  const isPublic = isPublicRoute(pathname);

  if (isPublic) {
    return NextResponse.next();
  }

  const accessToken = req.cookies[TOKEN_PATH];
  if (!accessToken) {
    return NextResponse.redirect(LOGIN_HREF);
  }

  const isValidToken = await checkAccessToken(accessToken);

  if (!isValidToken) {
    let res = NextResponse.redirect(LOGIN_HREF);
    res = removeCookie(res, TOKEN_PATH);
    return res;
  }

  return NextResponse.next();
}

How to verify the token

In my example, the checkAccessToken should verify the token (not decode, verify the signature).

This is where things are the most complicated imo.

When using the RSA256 algorithm

You also get a PUBLIC certificate (in addition to the SECRET key that must be... kept secret). Eventhough you do the check in the middleware, which is private and server-only code, that's good news because it means you could even use it in the browser, in theory.

So, you can either fetch the token validation endpoint provided by your auth server, or verify the token yourself. Fetching is not the recommended option because it might break Vercel/Next edge capabilities and add latency, according to the documentation.

I must admit that I did not succeed to verify the token yet using Next.js :) I'll update this answer if I manage to have a code sample that works.

When using a symmetrical encryption

You have only a PRIVATE secret passphrase. It means that the decoding have to happen server-side (good news, you are writing a middleware).

Login/logout

This doesn't change with middlewares. You store your access token as an httpOnly cookie. When logging out, you unset this cookie.

Managing those Set-Cookies headers are the responsibility of your auth server.

This is a basic workflow but it should work. You can then add a refresh token in the mix with a similar approach.

About token revokation

• If you verify the token in your middleware, there is no immediate revokation mechanism for the access token. Because there is no call to a database.

Therefore, in this scenario, you'd want to opt-in for short lived access token (eg 5 minutes) coupled with a refresh token. You can revoke the refresh token, so basically revoking works but takes a few minutes.

• If a 3rd party server verifies the token: then it could check for blacklisted tokens.

Caveats

Also, some piece of advice: most articles, tutorials etc. online are focused on server-to-server communication. Or client-to-API. They completely suck when it comes to check authentication before accessing web pages.

For instance, setting the Authorization header is not possible in the browser. It works only when communicating with an API. Cookies are mandatory for web pages.

Even then, if this API is meant to be called from a browser, it should preferably accept a cookie.

When discussing with experts on the field, you need to always clarify the Next.js use case.

Open questions: about session-based authentication

Some frameworks seem to prefer relying on the database. They store a hashed token in the db, which acts as a session. If you want to check auth, you need a server that will check the user's token against the stored token (= checking that there is an active session with this token).

I am thinking of Meteor for instance.

I couldn't find the name of this mechanism and its actual relation to JWT however. Are they simply variations of the JWT approach?

Next.js official authentication doc is not showing middlewares at the time of writing, but instead use getServerSideProps. I really don't like this pattern. It uses a kind of session system but I am not clear about the internals of it, I am not even sure of the name (is that session-based auth?).

Vercel edge handles examples shows how to secure an API route, but not a page (at the time of writing)