<?php

$jwt="/root/transcoder/jwt_key.json";
$token="eyJhbGciOiJIUzI1NiJ9.eyJjaGFsbGVuZ2UiOiI2ZmZjMjkwZDg0YjJhNzk2YWZiYmMxMTljMTZkYWViYjU3NTIxOTc5MWU3YWZlODMwMjI2MGIwYTVhMDNiZGQ0ZTU0NTRiNzg4ZDM2Mjk2YjQ0OTFiYjcxN2I0YjU4MzMiLCJleHAiOjE1NjEzNjU0ODcsImVtYWlsIjoiY3Jpc3RpQG5vdmFuZXQucm8ifQ.pGS4J_9sPafuJ78zAAkzh8VXlxy-XK2zv7Kvxs7Oo7g";

$key=get_key($jwt);

print("\ntoken: $token \nkey: $key\n");

if(validate($token, $key)) print("\nvalidate"); else print("\ninvalidate");
print("\n");


/////////////////////////////////////////////////////////

function get_key($jwt="/root/transcoder/jwt_key.json") {
        $j=file_get_contents($jwt);
        $json=json_decode($j, true);
        return $json["k"];
}

function urlsafeB64Decode($input) {
        $remainder = strlen($input) % 4;
        if ($remainder) {
                $padlen = 4 - $remainder;
                $input .= str_repeat('=', $padlen);
        }
        return base64_decode(strtr($input, '-_', '+/'));
}

function jsonDecode($input) {
        return json_decode($input, false, 512, JSON_BIGINT_AS_STRING);
}

function validate($token, $key){
        $tks = explode('.', $token);
        list($headb64, $bodyb64, $cryptob64) = $tks;

        $header = jsonDecode(urlsafeB64Decode($headb64));
        $payload = jsonDecode(jsonDecode($bodyb64));
        $sig = urlsafeB64Decode($cryptob64);

        $hash = hash_hmac("sha256", "$headb64.$bodyb64", urlsafeB64Decode($key), true);
        return hash_equals($sig, $hash);
}