get-jwks

get-jwks

Fetch utils for JWKS keys

Installation

npm install get-jwks

Usage

Options

const buildGetJwks = require('get-jwks')

const getJwks = buildGetJwks({
  max: 100,
  maxAge: 60 * 1000,
  allowedDomains: ['https://example.com'],
})

• max: Max items to hold in cache. Defaults to 100.
• maxAge: Milliseconds an item will remain in cache. Defaults to 60s.
• allowedDomains: Array of allowed domains. By default all domains are allowed.

max and maxAge are provided to lru-cache.

getJwk

const buildGetJwks = require('get-jwks')

const getJwks = buildGetJwks()

const jwk = await getJwks.getJwk({
  domain: 'https://exampe.com/',
  alg: 'token_alg',
  kid: 'token_kid',
})

Calling the asynchronous function getJwk will fetch the JSON Web Key, and verify if any of the public keys matches the provided alg and kid values. It will cache the matching key so if called again it will not make another request to retrieve a JWKS. It will also use a cache to store stale values which is used in case of errors as a fallback mechanism.

• domain: A string containing the domain (e.g. https://www.example.com/, with or without trailing slash) from which the library should fetch the JWKS. get-jwks will add the JWKS location (.well-known/jwks.json) to form the final url (ie: https://www.example.com/.well-known/jwks.json).
• alg: The alg header parameter represents the cryptographic algorithm used to secure the token. You will find it in your decoded JWT.
• kid: The kid is a hint that indicates which key was used to secure the JSON web signature of the token. You will find it in your decoded JWT.

getPublicKey

const buildGetJwks = require('get-jwks')

const getJwks = buildGetJwks()

const publicKey = await getJwks.getPublicKey({
  domain: 'https://exampe.com/',
  alg: 'token_alg',
  kid: 'token_kid',
})

Calling the asynchronous function getPublicKey will run the getJwk function to retrieve a matching key, then convert it to a PEM public key. It requires the same arguments as getJwk.

Integration Examples

This library can be easily used with other JWT libraries.

fastify-jwt

fastify-jwt is a Json Web Token plugin for Fastify.

The following example includes a scenario where you'd like to varify a JWT against a valid JWK on any request to your Fastify server. Any request with a valid JWT auth token in the header will return a successful response, otherwise will respond with an authentication error.

const Fastify = require('fastify')
const fjwt = require('fastify-jwt')
const buildGetJwks = require('get-jwks')

const fastify = Fastify()
const getJwks = buildGetJwks()

fastify.register(fjwt, {
  decode: { complete: true },
  secret: (request, token, callback) => {
    const {
      header: { kid, alg },
      payload: { iss },
    } = token
    getJwks
      .getPublicKey({ kid, domain: iss, alg })
      .then(publicKey => callback(null, publicKey), callback)
  },
})

fastify.addHook('onRequest', async (request, reply) => {
  await request.jwtVerify()
})

fastify.listen(3000)

fast-jwt

fast-jwt is a fast JSON Web Token implementation.

The following example shows how to use JWKS in fast-jwt via get-jwks.

const { createDecoder, createVerifier } = require('fast-jwt')
const buildGetJwks = require('get-jwks')

// JWT signed with JWKS
const token = '...'

// well known url of the token issuer
// often encoded as the `iss` property of the token payload
const domain = 'https://...'

// complete is necessary to get the header
const decode = createDecoder({ complete: true })

// decode the token and extract the header
const {
  header: { kid, alg },
} = decode(token)

const getJwks = buildGetJwks()
const publicKey = await getJwks.getPublicKey({ kid, domain, alg })

const verifyWithPromise = createVerifier({ key: publicKey })

// verify the token via the public key
const payload = await verifyWithPromise(token)