@fastify/auth NPM

@fastify/auth

This module does not provide an authentication strategy, but it provides a very fast utility to handle authentication (and multiple strategies) in your routes, without adding overhead.
Check out a complete example here.

Install

npm i @fastify/auth

Usage

As said above, @fastify/auth does not provide an authentication strategy, so you must provide authentication strategies yourself, with a decorator or another plugin.

In the following example, you will find a very simple implementation that should help you understand how to use this module:

fastify
  .decorate('verifyJWTandLevel', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .decorate('verifyUserAndPassword', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .register(require('@fastify/auth'))
  .after(() => {
    fastify.route({
      method: 'POST',
      url: '/auth-multiple',
      preHandler: fastify.auth([
        fastify.verifyJWTandLevel,
        fastify.verifyUserAndPassword
      ]),
      handler: (req, reply) => {
        req.log.info('Auth route')
        reply.send({ hello: 'world' })
      }
    })
  })

The default relationship of these customized authentication strategies is or, while we could also use and:

fastify
  .decorate('verifyAdmin', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .decorate('verifyReputation', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .register(require('@fastify/auth'))
  .after(() => {
    fastify.route({
      method: 'POST',
      url: '/auth-multiple',
      preHandler: fastify.auth([
        fastify.verifyAdmin,
        fastify.verifyReputation
      ], {
        relation: 'and'
      }),
      handler: (req, reply) => {
        req.log.info('Auth route')
        reply.send({ hello: 'world' })
      }
    })
  })

If you need composite authentication, such as verifying user account passwords and levels or meeting VIP eligibility criteria, you can use nested arrays. For example if you need the following logic: (verifyUserPassword and verifyLevel) or (verifyVIP), it can be achieved with the code below:

fastify
  .decorate('verifyUserPassword', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .decorate('verifyLevel', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .decorate('verifyVIP', function (request, reply, done) {
    // your validation logic
    done() // pass an error if the authentication fails
  })
  .register(require('@fastify/auth'))
  .after(() => {
    fastify.route({
      method: 'POST',
      url: '/auth-multiple',
      preHandler: fastify.auth([
        [fastify.verifyUserPassword, fastify.verifyLevel], // The arrays within an array have the opposite relation to the main (default) relation.
        fastify.verifyVIP
      ], {
        relation: 'or' // default relation
      }),
      handler: (req, reply) => {
        req.log.info('Auth route')
        reply.send({ hello: 'world' })
      }
    })
  })

If the relation (defaultRelation) parameter is and, then the relation inside sub-arrays will be or. If the relation (defaultRelation) parameter is or, then the relation inside sub-arrays will be and.

auth code	resulting logical expression
`fastify.auth([f1, f2, [f3, f4]], { relation: 'or' })`	`f1 OR f2 OR (f3 AND f4)`
`fastify.auth([f1, f2, [f3, f4]], { relation: 'and' })`	`f1 AND f2 AND (f3 OR f4)`

You can use the defaultRelation option while registering the plugin, to change the default relation:

fastify.register(require('@fastify/auth'), { defaultRelation: 'and'} )

For more examples, please check example-composited.js

This plugin support callback and Promise returned by the functions. Note that an async function does not have to call the done parameter, otherwise the route handler to which the auth methods are linked to might be called multiple times:

fastify
  .decorate('asyncVerifyJWTandLevel', async function (request, reply) {
    // your async validation logic
    await validation()
    // throws an error if the authentication fails
  })
  .decorate('asyncVerifyUserAndPassword', function (request, reply) {
    // return a promise that throws an error if the authentication fails
    return myPromiseValidation()
  })
  .register(require('@fastify/auth'))
  .after(() => {
    fastify.route({
      method: 'POST',
      url: '/auth-multiple',
      preHandler: fastify.auth([
        fastify.asyncVerifyJWTandLevel,
        fastify.asyncVerifyUserAndPassword
      ]),
      handler: (req, reply) => {
        req.log.info('Auth route')
        reply.send({ hello: 'world' })
      }
    })
  })

Keep in mind that route definition should either be done as a plugin or within an .after() callback. For a complete example implementation, see example.js.

@fastify/auth will run all your authentication methods and your request will continue if at least one succeeds, otherwise it will return an error to the client. Any successful authentication will automatically stop @fastify/auth from trying the rest, unless you provide the run: 'all' parameter:

fastify.route({
  method: 'GET',
  url: '/run-all',
  preHandler: fastify.auth([
    (request, reply, done) => { console.log('executed 1'); done() },
    (request, reply, done) => { console.log('executed 2'); done() },
    (request, reply, done) => { console.log('executed 3'); done(new Error('you are not authenticated')) },
    (request, reply, done) => { console.log('executed 4'); done() },
    (request, reply, done) => { console.log('executed 5'); done(new Error('you shall not pass')) }
  ], { run: 'all' }),
  handler: (req, reply) => { reply.send({ hello: 'world' }) }
})

This example will show all the console logs and will reply always with 401: you are not authenticated. The run parameter is useful if you are adding to the request business data read from auth-tokens.

You can use this plugin on route level as in the above example or on hook level by using the preHandler hook:

fastify.addHook('preHandler', fastify.auth([
  fastify.verifyJWTandLevel,
  fastify.verifyUserAndPassword
]))

fastify.route({
  method: 'POST',
  url: '/auth-multiple',
  handler: (req, reply) => {
    req.log.info('Auth route')
    reply.send({ hello: 'world' })
  }
})

The difference between the two approaches is that if you use the route level preHandler function the authentication will run just for the selected route. Whereas if you use the preHandler hook the authentication will run for all the routes declared inside the current plugin (and its descendants).

Security Considerations

`onRequest` vs. `preHandler` hook

The main difference between the onRequest and preHandler stages of the Fastify Lifecycle is that the body payload is not parsed in the onRequest stage. Parsing the body can be a potential security risk, as it can be used for denial of service (DoS) attacks. Therefore, it is recommended to avoid parsing the body for unauthorized access.

Using the @fastify/auth plugin in the preHandler hook can result in unnecessary memory allocation if a malicious user sends a large payload in the request body and the request is unauthorized. In this case, Fastify will parse the body, even though the request is not authorized, leading to unnecessary memory allocation. To avoid this, it is recommended to use the onRequest hook for authentication, if the authentication method does not require the request body, such as @fastify/jwt, which expects the authentication in the request header.

For authentication methods that do require the request body, such as sending a token in the body, you must use the preHandler hook.

In mixed cases you must use the preHandler hook.