JWT::createPemFromModulusAndExponent incorrect return value

libertyit1 commented 10 months ago

I retrieved JWKs for Google public keys from https://www.googleapis.com/oauth2/v3/certs including this one:

{
    "alg": "RS256",
    "kty": "RSA",
    "n": "hsYvCPtkUV7SIxwkOkJsJfhwV_CMdXU5i0UmY2QEs-Pa7v0-0y-s4EjEDtsQ8Yow6hc670JhkGBcMzhU4DtrqNGROXebyOse5FX0m0UvWo1qXqNTf28uBKB990mY42Icr8sGjtOw8ajyT9kufbmXi3eZKagKpG0TDGK90oBEfoGzCxoFT87F95liNth_GoyU5S8-G3OqIqLlQCwxkI5s-g2qvg_aooALfh1rhvx2wt4EJVMSrdnxtPQSPAtZBiw5SwCnVglc6OnalVNvAB2JArbqC9GAzzz9pApAk28SYg5a4hPiPyqwRv-4X1CXEK8bO5VesIeRX0oDf7UoM-pVAw",
    "use": "sig",
    "e": "AQAB",
    "kid": "838c06c62046c2d948affe137dd5310129f4d5d1"
}

JWT::createPemFromModulusAndExponent(n, e) with these values returns this PEM format:

JWTs from Google fail to verify using this key.

phpseclib3 and https://8gwifi.org/jwkconvertfunctions.jsp both return this PEM format:

and this key verifies Google JWTs correctly.

Wedrix commented 9 months ago

@libertyit1 did you figure out a fix for this? I seem to be facing the same/similar issue.

Could this be related to https://github.com/php/php-src/issues/11054

libertyit1 commented 9 months ago

@libertyit1 did you figure out a fix for this? I seem to be facing the same/similar issue.

Not in Firebase; I ended up importing phpseclib3 to convert the JWK e & n params into a PKCS8 key and used that in Firebase JWT::decode.

bshaffer commented 1 month ago

Hello and thank you for raising this issue.

In the official google/apiclient library, we do something similar (convert the certs to PKCS8 using phpseclib3 before passing them to JWT::decode). See here for an example.

However, I refactored this to use the current oauth2 certs for google at the URL you've provided, and this is working as expected without PHPseclib (see https://github.com/googleapis/google-api-php-client/pull/2596, where I refactor our Verify.php class to use CachedKeySet instead of phpseclib3)

So, TLDR, you should be able to use this library to verify Google keys without manually coverting to PKCS8 like this:

use Firebase\JWT\CachedKeySet;
use Firebase\JWT\JWT;
use Google\Auth\Cache\MemoryCacheItemPool;
use GuzzleHttp\Client;
use GuzzleHttp\Psr7\HttpFactory;

$keySet = new CachedKeySet(
    'https://www.googleapis.com/oauth2/v3/certs',
    new Client(),
    new HttpFactory(),
    new MemoryCacheItemPool(); // or some other PSR-6 cache
);

$payload = JWT::decode($idToken, $keySet);

libertyit1 commented 1 month ago

As a matter of interest, what was the bug in JWT::createPemFromModulusAndExponent? I don't see any changes to the code.

bshaffer commented 1 month ago

@libertyit1 I never confirmed there was an issue in JWT. The previous workaround (using phpseclib3) we had in the google client library was implemented well before the JWK logic was added to firebase/php-jwt.

So, maybe the bug hasn't been fixed, and the keys just got rotated so that it's no longer an issue? I am not really sure. Either way, I can't reproduce it.

bshaffer commented 1 month ago

@libertyit1 after some testing, using the values for module, exponent, and public key you provided, I was able to verify that this is parsing the keys as expected. I am not sure what changed to make this the case.

See https://github.com/firebase/php-jwt/pull/565

firebase / php-jwt

JWT::createPemFromModulusAndExponent incorrect return value #532