pem_to_jwt.rb

k = OpenSSL::PKey::RSA.new File.read 'private.pem'
pub = k.public_key
jwks = {
  "keys"=> [
    {
      "kty"=> "RSA",
      "use"=> "sig",
      "alg": "RS256",
      "kid"=> "pentesterlab",
      "n" => Base64.urlsafe_encode64(pub.n.to_s(2), padding: false),
      "e" => Base64.urlsafe_encode64(pub.e.to_s(2), padding: false)
    }
  ]
}