firebase/php-jwt

Facts and the checks behind them

Nothing below is copied from documentation. The check content/libraries/verify/firebase-php-jwt/run.sh ran firebase/php-jwt 7.2.1 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

  HS256HS384HS512RS256RS384RS512ES256ES384ES256KEdDSA

  HS256/384/512, RS256/384/512, ES256, ES384, ES256K and EdDSA signed and verified; ES512 and PS384/512 are not supported, and PS256 requires phpseclib.

  Recorded by the check

  fact jws-algorithms = HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, ES256K, EdDSA
  evidence jws-algorithms: PS256: DomainException: phpseclib/phpseclib is required for PS256 support
  evidence jws-algorithms: PS384: DomainException: Algorithm not supported
  evidence jws-algorithms: PS512: DomainException: Algorithm not supported
  evidence jws-algorithms: ES512: DomainException: Algorithm not supported
  evidence jws-algorithms: Ed25519: no key family

• 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 SignatureInvalidException: Signature verification failed.

  Recorded by the check

  fact jws-der-signature = rejected
  evidence jws-der-signature: Firebase\JWT\SignatureInvalidException: Signature verification failed

• Algorithm allow-list

  required

  decode() requires a Key object with an algorithm; a bare key string fails, and an RS256 token against new Key($ecPem, 'ES256') fails with Incorrect key for this algorithm.

  Recorded by the check

  fact jwt-algorithm-allowlist = required
  evidence jwt-algorithm-allowlist: RS256 token against new Key(EC PEM, 'ES256'): UnexpectedValueException: Incorrect key for this algorithm
  evidence jwt-algorithm-allowlist: decode() with a bare key string: UnexpectedValueException: "kid" empty, unable to lookup correct key

• Unsigned tokens (alg none)

  rejected

  An unsigned token fails with Algorithm not supported.

  Recorded by the check

  fact jwt-alg-none = rejected
  evidence jwt-alg-none: UnexpectedValueException: Algorithm not supported

• Public key used as an HMAC secret

  rejected

  An HS256 token keyed with the PEM text failed against the ES256 Key, but new Key($pem, 'HS256') verified it.

  Recorded by the check

  fact jwt-hmac-public-key = rejected
  evidence jwt-hmac-public-key: Key(PEM, 'ES256'): UnexpectedValueException: Incorrect key for this algorithm
  evidence jwt-hmac-public-key: Key(PEM, 'HS256') built by the application: ok

• Curve checked against alg

  not-enforced

  A token signed under ES256 with a P-384 key was produced and verified successfully.

  Recorded by the check

  fact jwt-ecdsa-curve-check = not-enforced
  evidence jwt-ecdsa-curve-check: ok

• Default clock skew

  0s

  JWT::$leeway is 0: a token expired three seconds earlier was rejected.

  Recorded by the check

  fact jwt-clock-skew = 0s
  evidence jwt-clock-skew: JWT::$leeway = 0

• Expiry claim required

  no

  A token without exp decoded successfully.

  Recorded by the check

  fact jwt-exp-required = no

• Short HMAC secret

  rejected

  A 5-byte HS256 key fails with Provided key is too short.

  Recorded by the check

  fact jwt-hmac-short-secret = rejected
  evidence jwt-hmac-short-secret: 5-byte HS256 key: DomainException: Provided key is too short

Usage

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

use Firebase\JWT\JWT;
use Firebase\JWT\Key;

$private = openssl_pkey_new(['private_key_type' => OPENSSL_KEYTYPE_EC, 'curve_name' => 'prime256v1']);
$publicPem = openssl_pkey_get_details($private)['key'];

$token = JWT::encode(['sub' => 'user-42', 'iss' => 'https://auth.example.com', 'exp' => time() + 600], $private, 'ES256');

// The Key object pins the algorithm; leeway is a static setting, 0 by default.
JWT::$leeway = 30;
$claims = JWT::decode($token, new Key($publicPem, 'ES256'));

// php-jwt checks exp/nbf/iat only when present and never checks iss or aud: do it here.
if (!isset($claims->exp) || $claims->iss !== 'https://auth.example.com') {
    throw new UnexpectedValueException('unexpected claims');
}
echo 'sub: ', $claims->sub, "\n";