lcobucci/jwt

Facts and the checks behind them

Nothing below is copied from documentation. The check content/libraries/verify/lcobucci-jwt/run.sh ran lcobucci/jwt 5.6.1 in the container image php:8.5.11-cli-trixie on October 20, 2026; the page must match what it printed, and each fact lists those lines.

• JWS algorithms

  HS256HS384HS512RS256RS384RS512ES256ES384ES512EdDSA

  HS, RS and ES at 256/384/512 and EdDSA signed and verified; there are no RSA-PSS or ES256K signer classes.

  Recorded by the check

  fact jws-algorithms = HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, ES512, EdDSA
  evidence jws-algorithms: PS256 signer class Lcobucci\JWT\Signer\Rsa\Pss\Sha256 exists: false
  evidence jws-algorithms: ES256K signer class Lcobucci\JWT\Signer\Ecdsa\Sha256K exists: false

• ES256 signature encoding

  raw

  ES256 signatures are 64 bytes of raw r‖s.

  Recorded by the check

  fact jws-ecdsa-encoding = raw

• DER signature inside a JWS

  rejected

  A DER-encoded ES256 signature fails with Token signature mismatch.

  Recorded by the check

  fact jws-der-signature = rejected
  evidence jws-der-signature: Lcobucci\JWT\Validation\RequiredConstraintsViolated: The token violates some mandatory constraints, details: - Token signature mismatch

• Algorithm allow-list

  required

  SignedWith pins the signer: an RS256 token against an ES256 signer failed with Token signer mismatch, and assert() without constraints throws NoConstraintsGiven.

  Recorded by the check

  fact jwt-algorithm-allowlist = required
  evidence jwt-algorithm-allowlist: RS256 token with SignedWith(ES256 signer, EC key): Lcobucci\JWT\Validation\RequiredConstraintsViolated: The token violates some mandatory constraints, details: - Token signer mismatch
  evidence jwt-algorithm-allowlist: assert() with no constraints: Lcobucci\JWT\Validation\NoConstraintsGiven: No constraint given.

• Unsigned tokens (alg none)

  rejected

  An unsigned token cannot be parsed: The JWT string is missing the Signature part.

  Recorded by the check

  fact jwt-alg-none = rejected
  evidence jwt-alg-none: parsing an unsigned token: Lcobucci\JWT\Token\InvalidTokenStructure: The JWT string is missing the Signature part

• Public key used as an HMAC secret

  rejected

  An HS256 token keyed with the PEM text failed SignedWith for the ES256 signer with Token signer mismatch.

  Recorded by the check

  fact jwt-hmac-public-key = rejected
  evidence jwt-hmac-public-key: SignedWith(ES256 signer, EC key): Lcobucci\JWT\Validation\RequiredConstraintsViolated: The token violates some mandatory constraints, details: - Token signer mismatch

• Curve checked against alg

  enforced

  The ES256 signer refused a P-384 key: The length of the provided key is different than 256 bits, 384 bits provided.

  Recorded by the check

  fact jwt-ecdsa-curve-check = enforced
  evidence jwt-ecdsa-curve-check: ES256 signer with a P-384 key: Lcobucci\JWT\Signer\InvalidKeyProvided: The length of the provided key is different than 256 bits, 384 bits provided

• Claims validated while decoding

  no

  Parsing and SignedWith do not check time: a token expired an hour earlier passed.

  Recorded by the check

  fact jwt-claims-validated-on-decode = no
  evidence jwt-claims-validated-on-decode: SignedWith only, token expired an hour ago: ok

• Default clock skew

  0s

  LooseValidAt and StrictValidAt allow no leeway unless given an interval.

  Recorded by the check

  fact jwt-clock-skew = 0s

• Expiry claim required

  no

  LooseValidAt accepted a token without exp; StrictValidAt requires iat, nbf and exp.

  Recorded by the check

  fact jwt-exp-required = no
  evidence jwt-exp-required: LooseValidAt without exp: ok; StrictValidAt: Lcobucci\JWT\Validation\RequiredConstraintsViolated: The token violates some mandatory constraints, details: - "Issued At" claim missing
  evidence jwt-exp-required: StrictValidAt with iat and exp but no nbf: Lcobucci\JWT\Validation\RequiredConstraintsViolated: The token violates some mandatory constraints, details: - "Not Before" claim missing

• Short HMAC secret

  rejected

  HS256 refused a 5-byte key: Key provided is shorter than 256 bits, only 40 bits provided.

  Recorded by the check

  fact jwt-hmac-short-secret = rejected
  evidence jwt-hmac-short-secret: 5-byte HS256 key: Lcobucci\JWT\Signer\InvalidKeyProvided: Key provided is shorter than 256 bits, only 40 bits provided

Usage

<?php
require 'vendor/autoload.php';

use Lcobucci\Clock\SystemClock;
use Lcobucci\JWT\Configuration;
use Lcobucci\JWT\Signer\Ecdsa\Sha256;
use Lcobucci\JWT\Signer\Key\InMemory;
use Lcobucci\JWT\Validation\Constraint\{IssuedBy, SignedWith, StrictValidAt};

$key = openssl_pkey_new(['private_key_type' => OPENSSL_KEYTYPE_EC, 'curve_name' => 'prime256v1']);
openssl_pkey_export($key, $privatePem);
$private = InMemory::plainText($privatePem);
$public = InMemory::plainText(openssl_pkey_get_details($key)['key']);

$config = Configuration::forAsymmetricSigner(new Sha256(), $private, $public);
$now = new DateTimeImmutable();
$token = $config->builder()->issuedBy('https://auth.example.com')->relatedTo('user-42')
    ->issuedAt($now)->canOnlyBeUsedAfter($now)->expiresAt($now->modify('+10 minutes'))
    ->getToken($config->signer(), $config->signingKey());

// Every check is an explicit constraint; StrictValidAt requires iat, nbf and exp.
$parsed = $config->parser()->parse($token->toString());
$config->validator()->assert($parsed,
    new SignedWith($config->signer(), $config->verificationKey()),
    new IssuedBy('https://auth.example.com'),
    new StrictValidAt(SystemClock::fromUTC(), new DateInterval('PT30S')));
echo 'sub: ', $parsed->claims()->get('sub'), "\n";