JSON Web Token

 

a.k.a  JWT

Robin CHALAS

@élao

github.com/chalasr

 JSON Web Token (JWT) is a compact, URL-safe means of representing
   claims to be transferred between two parties

RFC 7519

  • Compact

Fit into HTTP header, cookie, request body parameter or URI query argument

  • Self-contained

Work in Python, Go, Node.js, PHP, Ruby, Javascript, Java and Haskell

  • Cross-language

Includes all the required informations about itself, including what and why 

What does it look like?

 // String composed of 3 parts separated by dot 
 aaaaaaaaa.bbbbbbbbbbbbb.cccccc
 // Real world JWT
 eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9
 .eyJrZXkiOiJ2YWwiLCJpYXQiOjE0MjI2MDU0NDV9
 .eUiabuiKv-8PYk2AkGY4Fb5KMZeorYBLw261JPQD5lM
  • Header

Anatomy

// JWT's metadata
{
    "alg": "HS256", // the signature algorithm (here HMAC SHA-256)
    "typ": "JWT"    // the token type
}
  • Claims
// JWT's claims
{
    "user": "chalasr",   // user-related claim (custom)
    "iat": "1484246137", // issued at (standard)
    "exp": "1484249737"  // expiration (standard)
}
// JWT's Signature (HMAC SHA-256)
eUiabuiKv-8PYk2AkGY4Fb5KMZeorYBLw261JPQD5lM
  • Signature
 eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9         // header
 .eyJrZXkiOiJ2YWwiLCJpYXQiOjE0MjI2MDU0NDV9    // claims
 .eUiabuiKv-8PYk2AkGY4Fb5KMZeorYBLw261JPQD5lM // signature

Standard claims

iss (Issuer) Who delivered the JWT
sub (Subject) What is the subject of the JWT
aud (Audience) Who can process the JWT
exp (Expiration time) Until when is the JWT valid
nbf (Not before) From when can the JWT be processed
iat (Issued at) When the JWT has been delivered
jti (JWT ID) What is the JWT unique identifier
  • defined by the RFC
  • not mandatory
  • recommended to use
  • not relevant in all contexts

Those claims are:

Custom claims

Share information between parties that agree on using them

// Common custom claims
{
    "username": "chalasr",
    "roles": [
        "ROLE_USER",
    ]
}

In PHP

  • OpenSSL
  • phpseclib

Crypto engines

JOSE libraries

  • spomky-labs/jose

  • lcobucci/jwt

  • namshi/jose

  • firebase/php-jwt

* JOSE: Javascript Object Signing Encryption

Creation

// jwt.php
$base64UrlEncode = function (string $json) {
    return str_replace('=', '', strtr(base64_encode($json), '+/', '-_'));
};

$headers = json_encode(['typ' => 'JWT', 'alg' => 'RS256']);
$claims  = json_encode(['usr' => 'chalasr', 'exp' => time() + 3600, 'iat' => time()]);
$payload = [$base64UrlEncode($headers), $base64UrlEncode($claims)];

$privateKey = openssl_get_privatekey(file_get_contents(__DIR__.'/private.pem'), 'jwt-demo');
$signature = '';
openssl_sign(implode('.', $payload), $signature, $privateKey, OPENSSL_ALGO_SHA256);

$payload[] = $base64UrlEncode($signature);
$token = implode('.', $payload);

print $token; // JWT Created :)

$ php jwt.php

> eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9
.eyJrZXkiOiJ2YWwiLCJpYXQiOjE0MjI2MDU0NDV9
.eUiabuiKv-8PYk2AkGY4Fb5KMZeorYBLw261JPQD5lM

Verification

// verify.php
$base64UrlDecode = function (string $encoded) {
    if ($remainder = strlen($encoded) % 4) {
        $encoded .= str_repeat('=', 4 - $remainder);
    }

    return base64_decode(strtr($encoded, '-_', '+/'));
};

$token = $argv[1];
$payload = explode('.', $token);

$headers = (array) json_decode($base64UrlDecode($payload[0]));
$claims  = (array) json_decode($base64UrlDecode($payload[1]));
$signature = $base64UrlDecode($payload[2]);

$publicKey = openssl_get_publickey(file_get_contents('public.pem'));
$verified = openssl_verify($payload[0].'.'.$payload[1], $signature, $publicKey, OPENSSL_ALGO_SHA256);

if (!$verified || !isset($claims['exp']) || time() >= $claims['exp']) {
    die('Invalid JWT');
}

printf('Hello %s!', $claims['usr']); // JWT Verified :)
$ php verify.php eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9
  .eyJrZXkiOiJ2YWwiLCJpYXQiOjE0MjI2MDU0NDV9
  .eUiabuiKv-8PYk2AkGY4Fb5KMZeorYBLw261JPQD5lM

> Hello chalasr!

Signature/Encryption algorithms

  • asymmetric
  • symmetric

Symmetric cryptography is a cryptographic system in which both the sender and the receiver of a message share a single, common key that is used to encrypt and decrypt the message.
e.g: HS256 (HMAC)

Asymmetric cryptography is any cryptographic system that uses pairs of keys:  public keys which may be disseminated widely, and private keys which are known only to the owner.
e.g: RS256 (RSA)

In Symfony


$ composer require lexik/jwt-authentication-bundle

Demonstration

Thanks!

Slides: slides.com/chalasr/json-web-token

Sources: github.com/chalasr/jwt-prez

JSON Web Token

By Robin Chalas

JSON Web Token

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