require "base64"
require "jwt"

ISSUER_ID = "YOUR_ISSUER_ID"
KEY_ID = "YOUR PRIVATE KEY ID"

private_key = OpenSSL::PKey.read(File.read('path_to_your_private_key XXXXXXXXXXXX.p8'))


token = JWT.encode(
   {
    iss: ISSUER_ID,
    iat: XXXXXXXXXX, (registered claim key, whose value indicates the time at which the token was generated, in terms of the number of seconds since Epoch, in UTC)
    exp: XXXXXXXXXX  (registered claim key, whose value must not be greater than 15777000 (6 months in seconds) from the Current Unix Time on the server.)
   },
   private_key,
   "ES256",
   header_fields={
     kid: KEY_ID }
 )

puts token