Script to generate Apple Client secret

apple-gen-secret.mjs

#!/bin/node

import { SignJWT } from "jose"
import { createPrivateKey } from "crypto"

if (process.argv.includes("--help") || process.argv.includes("-h")) {
  console.log(`
  Creates a JWT from the components found at Apple.
  By default, the JWT has a 6 months expiry date.
  Read more: https://developer.apple.com/documentation/sign_in_with_apple/generate_and_validate_tokens#3262048

  Usage:
  node apple.mjs [--kid] [--iss] [--private_key] [--sub] [--expires_in] [--exp]
    
  Options:
    --help                 Print this help message
    --kid, --key_id        The key id of the private key
    --iss, --team_id       The Apple team ID
    --private_key          The private key to use to sign the JWT. (Starts with -----BEGIN PRIVATE KEY-----)
    --sub, --client_id     The client id to use in the JWT.
    --expires_in           Number of seconds from now when the JWT should expire. Defaults to 6 months.
    --exp                  Future date in seconds when the JWT expires
  `)
} else {
  const args = process.argv.slice(2).reduce((acc, arg, i) => {
    if (arg.match(/^--\w/)) {
      const key = arg.replace(/^--/, "").toLowerCase()
      acc[key] = process.argv[i + 3]
    }
    return acc
  }, {})

  const {
    team_id,
    iss = team_id,

    private_key,

    client_id,
    sub = client_id,

    key_id,
    kid = key_id,

    expires_in = 86400 * 180,
    exp = Math.ceil(Date.now() / 1000) + expires_in,
  } = args

  /**
   * How long is the secret valid in seconds.
   * @default 15780000
   */
  const expiresAt = Math.ceil(Date.now() / 1000) + expires_in
  const expirationTime = exp ?? expiresAt
  console.log(`
Apple client secret generated. Valid until: ${new Date(expirationTime * 1000)}

${await new SignJWT({})
  .setAudience("https://appleid.apple.com")
  .setIssuer(iss)
  .setIssuedAt()
  .setExpirationTime(expirationTime)
  .setSubject(sub)
  .setProtectedHeader({ alg: "ES256", kid })
  .sign(createPrivateKey(private_key.replace(/\\n/g, "\n")))}`)
}