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mock-jwks

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Readme

mock-jwks

A tool to mock a JWKS authentication service for development of microservices CONSUMING authentication and authorization jwts

Background

If you use jtws for authentication and authorization of your users against your microservices, you want to automatically unit test the authentication in your microservice for security. Happy and unhappy paths. Doing this while actually using a running JWKS deployment (like the auth0 backend) is slow and annoying, so e.g. auth0 suggest you mock their api. This turns out to be somewhat difficult, especially in the case of using RSA for signing of the tokens and not wanting to heavily dependency inject the middleware for authentication in your koa or express app. This is why I made this tool, which require less changes to your code.

Usage

Lets say you have a pretty standard koa app (I use a factory function to make the app, so I can scope nicely):

const Koa = require('koa')
const Router = require('koa-router')
const jwt = require('koa-jwt')
const jwksRsa = require('jwks-rsa')

const createApp = ({ jwksHost }) => {
  const app = new Koa()

  // We are setting up the jwksRsa client as usual (with production host)
  // We switch off caching to show how things work in ours tests.

  app.use(
    jwt({
      secret: jwksRsa.koaJwtSecret({
        cache: false,
        jwksUri: `${jwksHost}/.well-known/jwks.json`
      }),
      audience: 'private',
      issuer: 'master',
      algorithms: ['RS256']
    })
  )

  const router = new Router()

  // This route is protected by the authentication middleware
  router.get('/', ctx => {
    ctx.body = 'Authenticated!'
})

  app.use(router.middleware())
  return app
}

module.exports = createApp

You can easily unit test the authenticaion of this app like so:

const createJWKSMock = require('mock-jwks').default
const createApp = require('./index')
const supertest = require('supertest')

let server
let request
let jwksMock

describe('Some tests for authentication for our api', () => {
  beforeEach(async () => {
    // This creates the local PKI
    jwksMock = createJWKSMock('https://hardfork.eu.auth0.com')

    // We start our app.
    server = await createApp({
      jwksHost: 'https://hardfork.eu.auth0.com'
    }).listen()

    request = supertest(server)
  })
  afterEach(async () => {
    //This is just to avoid side effects between the tests.
    await server.close()
    await jwksMock.stop()
  })
  it('should not get access without correct token', async () => {
    // We start intercepting queries (see below)
    jwksMock.start()
    await request.get('/').expect(401)
  })
  it('should get access with mock token when jwksMock is running', async () => {
    // Again we start intercepting queries
    jwksMock.start()
    const access_token = jwksMock.token({
      aud: 'private',
      iss: 'master'
    })
    await request.get('/').set('Authorization' , `Bearer ${access_token}`).expect(200)
  })
  it('should not get access with mock token when jwksMock is not running', async () => {
    // Now we do not intercept queries. The queries of the middleware for the JKWS will
    // go to the production server and the local key will be invalid.
    const access_token = jwksMock.token({
      aud: 'private',
      iss: 'master'
    })
    await request.get('/').set('Authorization' , `Bearer ${access_token}`).expect(401)
  })
})

Under the hood

createJWKSMock will create a local PKI and generate a working JWKS.json. Calling jwksMock.start() will use nock to intercept all calls to `${jwksHost}/.well-known/jwks.json`. So when the jwks-rsa middleware gets a token to validate it will fetch the key to verify against from our local PKI instead of the production one and as such, the token is valid when signed with the local private key.