workers-jwt

@sagi.io/workers-jwt helps you generate a JWT on Cloudflare Workers with the WebCrypto API. Helper function for GCP Service Accounts included.

⭐ We use it at OpenSay to efficiently access Google's REST APIs with 1 round trip.

Installation

$ npm i @sagi.io/workers-jwt

API

We currently expose two methods: getToken for general purpose JWT generation and getTokenFromGCPServiceAccount for JWT generation using a GCP service account.

getToken({ ... })

Function definition:

const getToken = async ({
  privateKeyPEM,
  payload,
  alg = 'RS256',
  cryptoImpl = null,
  headerAdditions = {},
}) => { ... }

Where:

• privateKeyPEM is the private key string in PEM format.
• payload is the JSON payload to be signed, i.e. the { aud, iat, exp, iss, sub, scope, ... }.
• alg is the signing algorithm as defined in RFC7518, currently only RS256 and ES256 are supported.
• cryptoImpl is a WebCrypto API implementation. Cloudflare Workers support WebCrypto out of the box. For Node.js you can use [require('crypto').webcrypto - see examples below and in the tests.
• headerAdditions is an object with keys and string values to be added to the header of the JWT.

getTokenFromGCPServiceAccount({ ... })

Function definition:

const getTokenFromGCPServiceAccount = async ({
  serviceAccountJSON,
  aud,
  alg = 'RS256',
  cryptoImpl = null,
  expiredAfter = 3600,
  headerAdditions = {},
  payloadAdditions = {}
}) => { ... }

Where:

• serviceAccountJSON is the service account JSON object .
• aud is the audience field in the JWT's payload. e.g. https://www.googleapis.com/oauth2/v4/token'.
• expiredAfter - the duration of the token's validity. Defaults to 1 hour - 3600 seconds.
• payloadAdditions is an object with keys and string values to be added to the payload of the JWT. Example - { scope: 'https://www.googleapis.com/auth/chat.bot' }.
• alg, cryptoImpl, headerAdditions are defined as above.

Example

Suppose you'd like to use Firestore's REST API. The first step is to generate a service account with the "Cloud Datastore User" role. Please download the service account and store its contents in the SERVICE_ACCOUNT_JSON_STR environment variable.

The aud is defined by GCP's service definitions and is simply the following concatenated string: 'https://' + SERVICE_NAME + '/' + API__NAME. More info here.

For Firestore the aud is https://firestore.googleapis.com/google.firestore.v1.Firestore.

Cloudflare Workers Usage

Cloudflare Workers expose the crypto global for the Web Crypto API.

const { getTokenFromGCPServiceAccount } = require('@sagi.io/workers-jwt')

const serviceAccountJSON = await ENVIRONMENT.get('SERVICE_ACCOUNT_JSON','json')
const aud = `https://firestore.googleapis.com/google.firestore.v1.Firestore`

const token = await getTokenFromGCPServiceAccount({ serviceAccountJSON, aud} )

const headers = { Authorization: `Bearer ${token}` }

const projectId = 'example-project'
const collection = 'exampleCol'
const document = 'exampleDoc'

const docUrl =
  `https://firestore.googleapis.com/v1/projects/${projectId}/databases/(default)/documents`
  + `/${collection}/${document}`

const response = await fetch(docUrl, { headers })

const documentObj =  await response.json()

Node Usage (version <=14)

We use the node-webcrypto-ossl package to imitate the Web Crypto API in Node.

const { Crytpo }= require('node-webcrypto-ossl');
const cryptoImpl  = new Crypto();
const { getTokenFromGCPServiceAccount } = require('@sagi.io/workers-jwt')

const serviceAccountJSON = { ... }
const aud = `https://firestore.googleapis.com/google.firestore.v1.Firestore`

const token = await getTokenFromGCPServiceAccount({ serviceAccountJSON, aud, cryptoImpl } )

<... SAME AS CLOUDFLARE WORKERS ...>

Node Usage (version 15+)

Node 15 introduces the Web Crypto API. When using NextJS, you may need to pass in the native Node webcrypto lib to get both SSR and webpack to work during dev mode.

const { getTokenFromGCPServiceAccount } = require('@sagi.io/workers-jwt')

const serviceAccountJSON = { ... }
const aud = 'https://firestore.googleapis.com/google.firestore.v1.Firestore';

const token = await getTokenFromGCPServiceAccount({
  serviceAccountJSON,
  aud,
  cryptoImpl: globalThis.crypto || require('crypto').webcrypto,
});

<... SAME AS CLOUDFLARE WORKERS ...>