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fastify-cookie

CI NPM version Known Vulnerabilities js-standard-style

A plugin for Fastify that adds support for reading and setting cookies.

This plugin's cookie parsing works via Fastify's onRequest hook. Therefore, you should register it prior to any other onRequest hooks that will depend upon this plugin's actions.

fastify-cookie v2.x supports both Fastify@1 and Fastify@2. fastify-cookie v3 only supports Fastify@2.

Example

const fastify = require('fastify')()

fastify.register(require('fastify-cookie'), {
  secret: "my-secret", // for cookies signature
  parseOptions: {}     // options for parsing cookies
})

fastify.get('/', (req, reply) => {
  const aCookieValue = req.cookies.cookieName
  // `reply.unsingCookie()` is also available
  const bCookie = req.unsignCookie(req.cookies.cookieSigned);
  reply
    .setCookie('foo', 'foo', {
      domain: 'example.com',
      path: '/'
    })
    .cookie('baz', 'baz') // alias for setCookie
    .setCookie('bar', 'bar', {
      path: '/',
      signed: true
    })
    .send({ hello: 'world' })
})

TypeScript Example

import { FastifyCookieOptions } from 'fastify-cookie'
import cookie from 'fastify-cookie'
import fastify from 'fastify'

const app = fastify()

app.register(cookie, {
  secret: "my-secret", // for cookies signature
  parseOptions: {}     // options for parsing cookies
} as FastifyCookieOptions)

Options

  • secret (String | Array | Object):

    • A String can be passed to use as secret to sign the cookie using cookie-signature.
    • An Array can be passed if key rotation is desired. Read more about it in Rotating signing secret.
    • More sophisticated cookie signing mechanisms can be implemented by supplying an Object. Read more about it in Custom cookie signer.
  • parseOptions: An Object to pass as options to cookie parse.

API

Parsing

Cookies are parsed in the onRequest Fastify hook and attached to the request as an object named cookies. Thus, if a request contains the header Cookie: foo=foo then, within your handler, req.cookies.foo would equal 'foo'.

You can pass options to the cookie parse by setting an object named parseOptions in the plugin config object.

Sending

The method setCookie(name, value, options), and its alias cookie(name, value, options), are added to the reply object via the Fastify decorateReply API. Thus, in a request handler, reply.setCookie('foo', 'foo', {path: '/'}) will set a cookie named foo with a value of 'foo' on the cookie path /.

  • name: a string name for the cookie to be set
  • value: a string value for the cookie
  • options: an options object as described in the cookie serialize documentation with a extra param "signed" for signed cookie

Securing the cookie

Following are some of the precautions that should be taken to ensure the integrity of an application:

  • It's important to use options.httpOnly cookies to prevent attacks like XSS.
  • Use signed cookies (options.signed) to ensure they are not getting tampered with on client-side by an attacker.
  • Use __Host- Cookie Prefix to avoid Cookie Tossing attacks.
  • it's important to use HTTPS for your website/app to avoid a bunch of other potential security issues like MITM etc.

Clearing

The method clearCookie(name, options) is added to the reply object via the Fastify decorateReply API. Thus, in a request handler, reply.clearCookie('foo', {path: '/'}) will clear a cookie named foo on the cookie path /.

  • name: a string name for the cookie to be cleared
  • options: an options object as described in the cookie serialize documentation. Its optional to pass options object

Manual cookie parsing

The method parseCookie(cookieHeader) is added to the fastify instance via the Fastify decorate API. Thus, fastify.parseCookie('sessionId=aYb4uTIhdBXC') will parse the raw cookie header and return an object { "sessionId": "aYb4uTIhdBXC" }.

Rotating signing secret

Key rotation is when an encryption key is retired and replaced by generating a new cryptographic key. To implement rotation, supply an Array of keys to secret option.

Example:

fastify.register(require('fastify-cookie'), {
  secret: [key1, key2]
})

The plugin will always use the first key (key1) to sign cookies. When parsing incoming cookies, it will iterate over the supplied array to see if any of the available keys are able to decode the given signed cookie. This ensures that any old signed cookies are still valid.

Note:

  • Key rotation is only achieved by redeploying the server again with the new secret array.
  • Iterating through all secrets is an expensive process, so the rotation list should contain as few keys as possible. Ideally, only the current key and the most recently retired key.
  • Although previously signed cookies are valid even after rotation, cookies should be updated with the new key as soon as possible. See the following example for how to accomplish this.

Example:

fastify.get('/', (req, reply) => {
  const result = reply.unsignCookie(req.cookies.myCookie)

  if (result.valid && result.renew) {
    // Setting the same cookie again, this time plugin will sign it with a new key
    reply.setCookie('myCookie', result.value, {
      domain: 'example.com', // same options as before
      path: '/',
      signed: true
    })
  }
})

Custom cookie signer

The secret option optionally accepts an object with sign and unsign functions. This allows for implementing a custom cookie signing mechanism. See the following example:

Example:

fastify.register(require('fastify-cookie'), {
  secret: {
    sign: (value) => {
      // sign using custom logic
      return signedValue
    },
    unsign: (value) => {
      // unsign using custom logic
      return {
        valid: true, // the cookie has been unsigned successfully
        renew: false, // the cookie has been unsigned with an old secret
        value: 'unsignedValue'
      }
    }
  }
})

Manual cookie unsigning

The method unsignCookie(value) is added to the fastify instance and the reply object via the Fastify decorate & decorateReply APIs. Using it on a signed cookie will call the the provided signer's (or the default signer if no custom implementation is provided) unsign method on the cookie.

Example:

fastify.register(require('fastify-cookie'), { secret: 'my-secret' })

fastify.get('/', (req, rep) => {
  if (fastify.unsign(req.cookie.foo).valid === false) {
    rep.send('cookie is invalid')
    return
  }

  rep.send('cookie is valid')
})

License

MIT License