express-jwt

What is express-jwt?

The express-jwt package is a middleware for Express.js that allows you to validate JSON Web Tokens (JWTs) in your HTTP requests. It is commonly used for securing routes and ensuring that only authenticated users can access certain endpoints.

What are express-jwt's main functionalities?

JWT Validation

This feature allows you to validate JWTs in incoming requests. The middleware checks the token's validity and ensures it is signed with the correct secret key and algorithm.

const express = require('express');
const jwt = require('express-jwt');
const app = express();

const jwtMiddleware = jwt({
  secret: 'your-secret-key',
  algorithms: ['HS256']
});

app.use('/protected', jwtMiddleware, (req, res) => {
  res.send('This is a protected route');
});

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

Error Handling

This feature allows you to handle errors that occur during JWT validation. For example, you can send a 401 Unauthorized response if the token is invalid.

const express = require('express');
const jwt = require('express-jwt');
const app = express();

const jwtMiddleware = jwt({
  secret: 'your-secret-key',
  algorithms: ['HS256']
});

app.use('/protected', jwtMiddleware, (err, req, res, next) => {
  if (err.name === 'UnauthorizedError') {
    res.status(401).send('Invalid token');
  } else {
    next(err);
  }
});

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

Token Decoding

This feature allows you to decode the JWT and attach the payload to the request object. You can then access the decoded information in your route handlers.

const express = require('express');
const jwt = require('express-jwt');
const app = express();

const jwtMiddleware = jwt({
  secret: 'your-secret-key',
  algorithms: ['HS256'],
  requestProperty: 'auth'
});

app.use('/protected', jwtMiddleware, (req, res) => {
  res.send(`Hello, ${req.auth.name}`);
});

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

Other packages similar to express-jwt

jsonwebtoken

The jsonwebtoken package is a popular library for creating and verifying JSON Web Tokens. Unlike express-jwt, it does not provide middleware for Express.js, but it offers more flexibility for handling tokens in various contexts.

passport-jwt

The passport-jwt package is a Passport.js strategy for authenticating with a JSON Web Token. It integrates with Passport.js, a popular authentication middleware for Node.js, and provides more comprehensive authentication solutions compared to express-jwt.

koa-jwt

The koa-jwt package is similar to express-jwt but is designed for Koa.js applications. It provides middleware for validating JWTs in Koa.js, making it a suitable alternative for developers using the Koa framework.

README

express-jwt

This module provides Express middleware for validating JWTs (JSON Web Tokens) through the jsonwebtoken module. The decoded JWT payload is available on the request object.

Install

$ npm install express-jwt

API

expressjwt(options)

Options has the following parameters:

• secret: jwt.Secret | GetVerificationKey (required): The secret as a string or a function to retrieve the secret.
• getToken?: TokenGetter (optional): A function that receives the express Request and returns the token, by default it looks in the Authorization header.
• isRevoked?: IsRevoked (optional): A function to verify if a token is revoked.
• onExpired?: ExpirationHandler (optional): A function to handle expired tokens.
• credentialsRequired?: boolean (optional): If its false, continue to the next middleware if the request does not contain a token instead of failing, defaults to true.
• requestProperty?: string (optional): Name of the property in the request object where the payload is set. Default to req.auth.
• Plus... all the options available in the jsonwebtoken verify function.

The available functions have the following interface:

• GetVerificationKey = (req: express.Request, token: jwt.Jwt | undefined) => Promise<jwt.Secret>;
• IsRevoked = (req: express.Request, token: jwt.Jwt | undefined) => Promise<boolean>;
• TokenGetter = (req: express.Request) => string | Promise<string> | undefined;

Usage

Basic usage using an HS256 secret:

var { expressjwt: jwt } = require("express-jwt");
// or ES6
// import { expressjwt, ExpressJwtRequest } from "express-jwt";

app.get(
  "/protected",
  jwt({ secret: "shhhhhhared-secret", algorithms: ["HS256"] }),
  function (req, res) {
    if (!req.auth.admin) return res.sendStatus(401);
    res.sendStatus(200);
  }
);

The decoded JWT payload is available on the request via the auth property.

The default behavior of the module is to extract the JWT from the Authorization header as an OAuth2 Bearer token.

Required Parameters

The algorithms parameter is required to prevent potential downgrade attacks when providing third party libraries as secrets.

:warning: Do not mix symmetric and asymmetric (ie HS256/RS256) algorithms: Mixing algorithms without further validation can potentially result in downgrade vulnerabilities.

jwt({
  secret: "shhhhhhared-secret",
  algorithms: ["HS256"],
  //algorithms: ['RS256']
});

Additional Options

You can specify audience and/or issuer as well, which is highly recommended for security purposes:

jwt({
  secret: "shhhhhhared-secret",
  audience: "http://myapi/protected",
  issuer: "http://issuer",
  algorithms: ["HS256"],
});

If the JWT has an expiration (exp), it will be checked.

If you are using a base64 URL-encoded secret, pass a Buffer with base64 encoding as the secret instead of a string:

jwt({
  secret: Buffer.from("shhhhhhared-secret", "base64"),
  algorithms: ["RS256"],
});

To only protect specific paths (e.g. beginning with /api), use express router call use, like so:

app.use("/api", jwt({ secret: "shhhhhhared-secret", algorithms: ["HS256"] }));

Or, the other way around, if you want to make some paths unprotected, call unless like so.

app.use(
  jwt({
    secret: "shhhhhhared-secret",
    algorithms: ["HS256"],
  }).unless({ path: ["/token"] })
);

This is especially useful when applying to multiple routes. In the example above, path can be a string, a regexp, or an array of any of those.

For more details on the .unless syntax including additional options, please see express-unless.

This module also support tokens signed with public/private key pairs. Instead of a secret, you can specify a Buffer with the public key

var publicKey = fs.readFileSync("/path/to/public.pub");
jwt({ secret: publicKey, algorithms: ["RS256"] });

Customizing Token Location

A custom function for extracting the token from a request can be specified with the getToken option. This is useful if you need to pass the token through a query parameter or a cookie. You can throw an error in this function and it will be handled by express-jwt.

app.use(
  jwt({
    secret: "hello world !",
    algorithms: ["HS256"],
    credentialsRequired: false,
    getToken: function fromHeaderOrQuerystring(req) {
      if (
        req.headers.authorization &&
        req.headers.authorization.split(" ")[0] === "Bearer"
      ) {
        return req.headers.authorization.split(" ")[1];
      } else if (req.query && req.query.token) {
        return req.query.token;
      }
      return null;
    },
  })
);

Retrieve key dynamically

If you need to obtain the key dynamically from other sources, you can pass a function in the secret parameter with the following parameters:

• req (Object) - The express request object.
• token (Object) - An object with the JWT payload and headers.

For example, if the secret varies based on the issuer:

var jwt = require("express-jwt");
var data = require("./data");
var utilities = require("./utilities");

var getSecret = async function (req, token) {
  const issuer = token.payload.iss;
  const tenant = await data.getTenantByIdentifier(issuer);
  if (!tenant) {
    throw new Error("missing_secret");
  }
  return utilities.decrypt(tenant.secret);
};

app.get(
  "/protected",
  jwt({ secret: getSecret, algorithms: ["HS256"] }),
  function (req, res) {
    if (!req.auth.admin) return res.sendStatus(401);
    res.sendStatus(200);
  }
);

Secret rotation

The getSecret callback could also be used in cases where the same issuer might issue tokens with different keys at certain point:

var getSecret = async function (req, token) {
  const { iss } = token.payload;
  const { kid } = token.header;
  // get the verification key by a given key-id and issuer.
  return verificationKey;
};

Revoked tokens

It is possible that some tokens will need to be revoked so they cannot be used any longer. You can provide a function as the isRevoked option. The signature of the function is function(req, payload, done):

• req (Object) - The express request object.
• token (Object) - An object with the JWT payload and headers.

For example, if the (iss, jti) claim pair is used to identify a JWT:

const jwt = require("express-jwt");
const data = require("./data");

const isRevokedCallback = async (req, token) => {
  const issuer = token.payload.iss;
  const tokenId = token.payload.jti;
  const token = await data.getRevokedToken(issuer, tokenId);
  return token !== "undefined";
};

app.get(
  "/protected",
  jwt({
    secret: "shhhhhhared-secret",
    algorithms: ["HS256"],
    isRevoked: isRevokedCallback,
  }),
  function (req, res) {
    if (!req.auth.admin) return res.sendStatus(401);
    res.sendStatus(200);
  }
);

Handling expired tokens

You can handle expired tokens as follows:

  jwt({
    secret: "shhhhhhared-secret",
    algorithms: ["HS256"],
    onExpired: async (req, err) => {
      if (new Date() - err.inner.expiredAt < 5000) { return;}
      throw err;
    },,
  })

Error handling

The default behavior is to throw an error when the token is invalid, so you can add your custom logic to manage unauthorized access as follows:

app.use(function (err, req, res, next) {
  if (err.name === "UnauthorizedError") {
    res.status(401).send("invalid token...");
  } else {
    next(err);
  }
});

You might want to use this module to identify registered users while still providing access to unregistered users. You can do this by using the option credentialsRequired:

app.use(
  jwt({
    secret: "hello world !",
    algorithms: ["HS256"],
    credentialsRequired: false,
  })
);

Typescript

A Request type is provided from express-jwt, which extends express.Request with the auth property. It could be aliased, like how JWTRequest is below.

import { expressjwt, Request as JWTRequest } from "express-jwt";

app.get(
  "/protected",
  expressjwt({ secret: "shhhhhhared-secret", algorithms: ["HS256"] }),
  function (req: JWTRequest, res: express.Response) {
    if (!req.auth?.admin) return res.sendStatus(401);
    res.sendStatus(200);
  }
);

Migration from v6

1. The middleware function is now available as a named import rather than a default one: import { expressjwt } from 'express-jwt'
2. The decoded JWT payload is now available as req.auth rather than req.user
3. The secret function had (req, header, payload, cb), now it can return a promise and receives (req, token). token has header and payload.
4. The isRevoked function had (req, payload, cb), now it can return a promise and receives (req, token). token has header and payload.

Related Modules

• jsonwebtoken — JSON Web Token sign and verification
• express-jwt-permissions - Permissions middleware for JWT tokens

Tests

$ npm install
$ npm test

Contributors

Check them out here

Issue Reporting

If you have found a bug or if you have a feature request, please report them at this repository issues section. Please do not report security vulnerabilities on the public GitHub issue tracker. The Responsible Disclosure Program details the procedure for disclosing security issues.

Author

Auth0

License

This project is licensed under the MIT license. See the LICENSE file for more info.