cookie-signature-subtle

> Sign and unsign cookies using web standard SubtleCrypto (browser-compatible)


This library makes it easy to sign response cookie values and authenticate request cookie values using a shared secret. Although the intent is to handle cookie values for your application, this library doesn't work directly with request or response headers, and it can be used for signing/authenticating any simple strings.

This is a rewrite of the original cookie-signature package that uses the SubtleCrypto standard of the modern Web Crypto API instead of the Node.js-specific crypto module, for better compatibility with runtimes like Vercel's Edge Runtime. It shares the same API contract as cookie-signature except that the methods are asynchronous (returning a Promise) instead of synchronous, due to the nature of the SubtleCrypto API.

This library is meant to be compatible with web standards and modern runtimes. Although it should be compatible with a browser environment/runtime, it is generally not a good idea to expose secrets used for generating digital signatures to code running on a client's browser.

See below for usage and examples.

Install

``console
$ npm i cookie-signature-subtle
`

`js
// default export for standard use
import signature from 'cookie-signature-subtle'

const secret = 'not a good secret'

const signedValue = await signature.sign('cookievalue', secret)
// => 'cookievalue.XAn8/gvhqwlDLy7ibUMVNWlXpQetHJJFQ9cz6u9Oeeg'

const originalValue = await signature.unsign(signedValue, secret)
// => 'cookievalue'

const bogusValue = await signature.unsign('not valid', secret)
// => false

const bogusSecret = await signature.unsign(signedValue, 'another bad secret')
// => false
`

`js
// named export for customization
import { CookieSignature } from 'cookie-signature-subtle'

const signature = CookieSignature.get({ separator: '_', hash: 'SHA-512' })
const secret = 'not a good secret'

const signedValue = await signature.sign('cookievalue', secret)
// => 'cookievalue_/8OaZNevtP9If8FmWIbA6AWo9Tuowu/GXnYQ90VvzztyQzNCsLCBnRbVXIuqE3bUCahmlXhHN33zNAdWm55azw'

const originalValue = await signature.unsign(signedValue, secret)
// => 'cookievalue'

const bogusValue = await signature.unsign('not valid', secret)
// => false

const bogusSecret = await signature.unsign(signedValue, 'another bad secret')
// => false
`

API

The default export is an instance of the CookieSignature class configured with default options that are compatible with the original cookie-signature package except that the methods of this library are async (return a Promise). Otherwise the API contract is the same as cookie-signature.

The main API methods are:

- signature.sign(valueToSign, secret)

Sign the given string with a signature derived from the given secret.

valueToSign must be a string; otherwise this method rejects (throws) with a TypeError.

secret may be a string, Buffer, TypedArray, CryptoKey, or anything accepted by importKey. It cannot be null or undefined; otherwise this method rejects (throws) with a TypeError.

Returns a Promise that resolves to a string containing the given value concatenated with a separator ('.' by default) and the HMAC signature (a sha256 hash by default) encoded as base64 without any padding. The returned value can be provided to the unsign method with the same secret to validate its authenticity and be converted back to the original unsigned value.

Example:

`js
import signature from 'cookie-signature-subtle'

const signedValue = await signature.sign('hello', 'not a good secret')
// => 'hello.6J710tYHo2C2ka+uG9bw9xol/u3K+Is1FVaOyNlAiBE'
`

- signature.unsign(signedCookieValue, secret)

Convert an authenticated/signed string value back into its original unsigned string value.

signedCookieValue must be a string; otherwise this method rejects (throws) with a TypeError.

secret may be a string, Buffer, TypedArray, CryptoKey, or anything accepted by importKey. It cannot be null or undefined; otherwise this method rejects (throws) with a TypeError.

Returns a Promise that resolves to either the unsigned string value (if authenticated) or the boolean value false (if not authenticated).

Example:

`js
import signature from 'cookie-signature-subtle'

const originalValue = await signature.unsign('hello.6J710tYHo2C2ka+uG9bw9xol/u3K+Is1FVaOyNlAiBE', 'not a good secret')
// => 'hello'

const bogusValue = await signature.unsign('not valid', 'not a good secret')
// => false
`

This module also exports the CookieSignature class as a named export if you'd like to customize the separator or hash algorithm used. You can construct your own signature instance using the constructor (i.e. new CookieSignature(opts)) or a static get convenience method (i.e. CookieSignature.get(opts)).

The options accepted when constructing a new instance are:

- opts.separator (string, default '.'): the string used to separate the unsigned value from the signature in the signed value

Must be a string; otherwise the given option will be ignored and '.' will be used.

Since the signature is always a base64-encoded string, make sure you use a separator that will never be part of the encoded signature (i.e. don't use a-z, A-Z, 0-9, '+', or '/').

Example:

`js
import { CookieSignature } from 'cookie-signature-subtle'
const signature = CookieSignature.get({ separator: '_' })

const signedValue = await signature.sign('hello', 'not a good secret')
// => 'hello_6J710tYHo2C2ka+uG9bw9xol/u3K+Is1FVaOyNlAiBE'

const originalValue = await signature.unsign(signedValue, 'not a good secret')
// => 'hello'
`

- opts.hash (string, default 'SHA-256'): the hashing algorithm to use when generating the signature

Per the SubtleCrypto API, accepts values 'SHA-1', 'SHA-256', 'SHA-384', or 'SHA-512'. If an unknown value is given, it will be ignored and 'SHA-256' will be used.

Example:

`js
import { CookieSignature } from 'cookie-signature-subtle'
const signature = CookieSignature.get({ hash: 'SHA-384' })

const signedValue = await signature.sign('hello', 'not a good secret')
// => 'hello.6J0vmMamuPKikY6ufK/uE6oqE75/7GwjtixxVss8MBGtLv07L9UuiAFjHhU7wPyA'

const originalValue = await signature.unsign(signedValue, 'not a good secret')
// => 'hello'
``

License

ISC © Andrew Goode