universal-github-app-jwt

Calculate GitHub App bearer tokens for Node, Deno, and modern browsers

Usage

Browsers

Load universal-github-app-jwt directly from esm.sh

<script type="module">
import githubAppJwt from "https://esm.sh/universal-github-app-jwt";
</script>

Node

Install with npm install universal-github-app-jwt

import githubAppJwt from "universal-github-app-jwt";

Deno

Load universal-github-app-jwt directly from esm.sh, including types.

import githubAppJwt from "https://esm.sh/universal-github-app-jwt";

const { token, appId, expiration } = await githubAppJwt({
  id: APP_ID,
  privateKey: PRIVATE_KEY,
});

The retrieved token can now be used in Authorization request header, e.g. with @octokit/request:

request("GET /app", {
  headers: {
    authorization: `bearer ${token}`,
  },
});

For a complete implementation of GitHub App authentication strategies, see @octokit/auth-app.js.

`githubAppJwt(options)`

name	type	description
`options.id`	`number \| string`	Required. The GitHub App's ID or Client ID. For `github.com` and GHES 3.14+, it is recommended to use the Client ID.
`options.privateKey`	`string`	Required. Content of the `*.pem` file you downloaded from the app’s about page. You can generate a new private key if needed. Make sure to preserve the line breaks. If your private key contains escaped newlines (`\\n`), they will be automatically replaced with actual newlines.
`options.now`	`number`	An optional override for the current time in seconds since the UNIX epoch. Defaults to `Math.floor(Date.now() / 1000))`. This value can be overridden to account for a time skew between the local machine and the authentication server.

githubAppJwt(options) resolves with an object with the following keys

name	type	description
`token`	`string`	The JSON Web Token (JWT) to authenticate as the app.
`appId`	`number`	The GitHub App database ID or Client ID passed in `options.id`.
`expiration`	`number`	Timestamp as UNIX epoch, e.g. `1530922170`. A Date object can be created using `new Date(authentication.expiration)`.

About Private Key formats

When downloading a private-key.pem file from GitHub, the format is in PKCS#1 format. Unfortunately, the WebCrypto API only supports PKCS#8.

If you use 1Password to store a private key as an SSH key, it will be transformed to the OpenSSH format, which is also not supported by WebCrypto.

You can identify the format based on the the first line

First Line	Format
`-----BEGIN RSA PRIVATE KEY-----`	PKCS#1
`-----BEGIN PRIVATE KEY-----`	PKCS#8
`-----BEGIN OPENSSH PRIVATE KEY-----`	OpenSSH

Converting `PKCS#1` to `PKCS#8`

Using an Online Private Key Converter

Convert quickly using the Web interface at https://private-key-converter.vercel.app

Using Node.js

If you use Node.js, you can convert the format before passing it to universal-github-app-jwt:

import crypto from "node:crypto";
import githubAppJwt from "universal-github-app-jwt";

const privateKeyPkcs8 = crypto
  .createPrivateKey(process.env.PRIVATE_KEY)
  .export({
    type: "pkcs8",
    format: "pem",
  });

const { token, appId, expiration } = await githubAppJwt({
  id: process.env.APP_ID,
  privateKey: privateKeyPkcs8,
});

Using OpenSSL

Convert the format using openssl before passing it to your app.

openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in private-key.pem -out private-key-pkcs8.key

Converting `OpenSSH` to `PKCS#8`

cp private-key.pem private-key-pkcs8.key && ssh-keygen -p -m PKCS8  -N "" -f private-key-pkcs8.key

This command forces a format change by asking ssh-keygen to set no password and then output in a different format.

I'm looking for help to create a minimal OpenSSH to PKCS convert library that I can recommend people to use before passing the private key to githubAppJwt. Please create an issue if you'd like to help.

License

MIT

Package detail