generate-jwt.php

<?php
$key = '###############';

$exp = ( new DateTime( "now" ) )->getTimestamp() + 120;

$header = [
  'typ' => 'JWT',
  'alg' => 'HS256'
];

$header = json_encode( $header );
$header = base64url_encode( $header );

$payload = [
  'iss' => '###############',
  'exp' => $exp,
];
$payload = json_encode( $payload );
$payload = base64url_encode( $payload );

$signature = hash_hmac( 'sha256', "{$header}.{$payload}", $key, true );
$signature = base64url_encode( $signature );

$token = "{$header}.{$payload}.{$signature}";
return $token;