@fastify/cookie

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.

It is also possible to import the low-level cookie parsing and serialization functions.

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

Installation

npm i @fastify/cookie

or

yarn add @fastify/cookie

Example

const fastify = require('fastify')()

fastify.register(require('@fastify/cookie'), {
  secret: "my-secret", // for cookies signature
  hook: 'onRequest', // set to false to disable cookie autoparsing or set autoparsing on any of the following hooks: 'onRequest', 'preParsing', 'preHandler', 'preValidation'. default: 'onRequest'
  parseOptions: {}  // options for parsing cookies
})

fastify.get('/', (req, reply) => {
  const aCookieValue = req.cookies.cookieName
  // `reply.unsignCookie()` 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 type { 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)

Importing serialize and parse

const { serialize, parse } = require('@fastify/cookie')
const fastify = require('fastify')()

fastify.get('/', (req, reply) => {
  const cookie = serialize('lang', 'en', {
    maxAge: 60_000,
  })

  reply.header('Set-Cookie', cookie)

  reply.send('Language set!')
})

Options

• secret (String | Array | Buffer | Object):

  • A String or Buffer 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.

• hook: the Fastify Hook to register the parsing of cookie into. Default: onRequest.

• algorithm: the algorithm to use to sign the cookies. Default: sha256.

• parseOptions: An Object to modify the serialization of set cookies.

:warning: Security Considerations :warning:

It is recommended to use sha256 or stronger hashing algorithm as well as a secret that is at least 20 bytes long.

parseOptions

domain

Specifies the value for the Domain Set-Cookie attribute. By default, no domain is set, and most clients will consider the cookie to apply to only the current domain.

encode

Specifies a function that will be used to encode a cookie's value. Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode a value into a string suited for a cookie's value.

The default function is the global encodeURIComponent, which will encode a JavaScript string into UTF-8 byte sequences and then URL-encode any that fall outside of the cookie range.

expires

Specifies the Date object to be the value for the Expires Set-Cookie attribute. By default, no expiration is set, and most clients will consider this a "non-persistent cookie" and will delete it on a condition like exiting a web browser application.

Note: the cookie storage model specification states that if both expires and maxAge are set, then maxAge takes precedence, but it is possible not all clients by obey this, so if both are set, they should point to the same date and time.

httpOnly

Specifies the boolean value for the HttpOnly Set-Cookie attribute. When truthy, the HttpOnly attribute is set, otherwise it is not. By default, the HttpOnly attribute is not set.

Note: be careful when setting this to true, as compliant clients will not allow client-side JavaScript to see the cookie in document.cookie.

maxAge

Specifies the number (in seconds) to be the value for the Max-Age Set-Cookie attribute. The given number will be converted to an integer by rounding down. By default, no maximum age is set.

Note: the cookie storage model specification states that if both expires and maxAge are set, then maxAge takes precedence, but it is possible not all clients by obey this, so if both are set, they should point to the same date and time.

partitioned

Specifies the boolean value for the Partitioned Set-Cookie attribute. When truthy, the Partitioned attribute is set, otherwise it is not. By default, the Partitioned attribute is not set.

⚠️ Warning: This is an attribute that has not yet been fully standardized, and may change in the future without reflecting the semver versioning. This also means many clients may ignore the attribute until they understand it.

More information about can be found in the proposal.

priority

Specifies the string to be the value for the Priority Set-Cookie attribute.

• 'low' will set the Priority attribute to Low.
• 'medium' will set the Priority attribute to Medium, the default priority when not set.
• 'high' will set the Priority attribute to High.

More information about the different priority levels can be found in the specification.

⚠️ Warning: This is an attribute that has not yet been fully standardized, and may change in the future without reflecting the semver versioning. This also means many clients may ignore the attribute until they understand it.

path

Specifies the value for the Path Set-Cookie attribute. By default, the path is considered the "default path".

sameSite

Specifies the boolean or string to be the value for the SameSite Set-Cookie attribute.

• true will set the SameSite attribute to Strict for strict same site enforcement.
• false will not set the SameSite attribute.
• 'lax' will set the SameSite attribute to Lax for lax same site enforcement.
• 'none' will set the SameSite attribute to None for an explicit cross-site cookie.
• 'strict' will set the SameSite attribute to Strict for strict same site enforcement.

More information about the different enforcement levels can be found in the specification.

Note: This is an attribute that has not yet been fully standardized, and may change in the future. This also means many clients may ignore this attribute until they understand it.

secure

Specifies the boolean value for the Secure Set-Cookie attribute. When truthy, the Secure attribute is set, otherwise it is not. By default, the Secure attribute is not set.

Note: be careful when setting this to true, as compliant clients will not send the cookie back to the server in the future if the browser does not have an HTTPS connection.

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
• options.signed: the cookie should be signed
• options.secure: if set to true it will set the Secure-flag. If it is set to "auto" Secure-flag is set when the connection is using tls.

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, to the request and the reply object via the Fastify decorate, decorateRequest and decorateReply APIs, if a secret was provided as option. 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.unsignCookie(req.cookie.foo).valid === false) {
    rep.send('cookie is invalid')
    return
  }

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

Other cases of manual signing

Sometimes the service under test should only accept requests with signed cookies, but it does not generate them itself.

Example:

test('Request requires signed cookie', async () => {
    const response = await app.inject({
        method: 'GET',
        url: '/',
        headers: {
          cookies : {
            'sid': app.signCookie(sidValue)
          }
        },
    });

    expect(response.statusCode).toBe(200);
});

Manual signing/unsigning with low level utilities

with Signer

const { Signer } = require('@fastify/cookie');

const signer = new Signer('secret');
const signedValue = signer.sign('test');
const {valid, renew, value } = signer.unsign(signedValue);

with sign/unsign utilities

const { fastifyCookie } = require('@fastify/cookie');

const signedValue = fastifyCookie.sign('test', 'secret');
const unsignedvalue = fastifyCookie.unsign(signedValue, 'secret');

License

MIT License