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	Required. Find App ID on the app’s about page in settings.
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.
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 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 -m PKCS8  -N "" -f private-key-pkcs8.key

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