Garage-SDKs/garage_iap/test/jwks_verify_test.dart

import "dart:convert";
import "dart:typed_data";

import "package:flutter_test/flutter_test.dart";
import "package:garage_iap/src/jwks_verify.dart";
import "package:garage_iap/src/models.dart";
import "package:pointycastle/export.dart";

String _b64uBig(BigInt n) {
  final bytes = <int>[];
  var v = n;
  while (v > BigInt.zero) {
    bytes.insert(0, (v & BigInt.from(0xff)).toInt());
    v = v >> 8;
  }
  return base64Url.encode(Uint8List.fromList(bytes)).replaceAll("=", "");
}

String _b64uStr(String s) =>
    base64Url.encode(utf8.encode(s)).replaceAll("=", "");

String _b64uBytes(List<int> b) => base64Url.encode(b).replaceAll("=", "");

AsymmetricKeyPair<PublicKey, PrivateKey> _genKey(int seed) {
  final rng = SecureRandom("Fortuna")
    ..seed(KeyParameter(
        Uint8List.fromList(List.generate(32, (i) => (i + seed) & 0xff))));
  final gen = RSAKeyGenerator()
    ..init(ParametersWithRandom(
        RSAKeyGeneratorParameters(BigInt.parse("65537"), 2048, 64), rng));
  return gen.generateKeyPair();
}

// build a compact RS256 JWT the same way the backend does — header.payload
// signed with PKCS1v15 SHA-256.
String _signJwt(RSAPrivateKey priv, Map<String, dynamic> header,
    Map<String, dynamic> payload) {
  final h = _b64uStr(jsonEncode(header));
  final p = _b64uStr(jsonEncode(payload));
  final input = utf8.encode("$h.$p");
  final signer = Signer("SHA-256/RSA") as RSASigner;
  signer.init(true, PrivateKeyParameter<RSAPrivateKey>(priv));
  final sig = signer.generateSignature(Uint8List.fromList(input));
  return "$h.$p.${_b64uBytes(sig.bytes)}";
}

void main() {
  test("verifies a signed licence and reads products", () {
    final pair = _genKey(1);
    final pub = pair.publicKey as RSAPublicKey;
    final priv = pair.privateKey as RSAPrivateKey;

    final jwks = {
      "keys": [
        {
          "kty": "RSA",
          "use": "sig",
          "alg": "RS256",
          "kid": "k1",
          "n": _b64uBig(pub.modulus!),
          "e": _b64uBig(pub.exponent!)
        }
      ]
    };

    final now = DateTime.now().toUtc();
    final token = _signJwt(priv, {
      "alg": "RS256",
      "kid": "k1"
    }, {
      "sub": "user-123",
      "app": "my-app",
      "products": [
        {"sku": "pro", "kind": "app"}
      ],
      "exp": now.add(const Duration(hours: 24)).millisecondsSinceEpoch ~/ 1000,
    });

    final lic = verifyLicence(token, jwks,
        expectedApp: "my-app", expectedSub: "user-123");
    expect(lic.grants("pro"), isTrue);
    expect(lic.grants("nope"), isFalse);
    expect(lic.isExpired, isFalse);
  });

  test("rejects wrong app, wrong sub, and a tampered signature", () {
    final pair = _genKey(7);
    final pub = pair.publicKey as RSAPublicKey;
    final priv = pair.privateKey as RSAPrivateKey;
    final jwks = {
      "keys": [
        {
          "kty": "RSA",
          "kid": "k1",
          "alg": "RS256",
          "n": _b64uBig(pub.modulus!),
          "e": _b64uBig(pub.exponent!)
        }
      ]
    };

    final now = DateTime.now().toUtc();
    final exp =
        now.add(const Duration(hours: 1)).millisecondsSinceEpoch ~/ 1000;
    final good = _signJwt(priv, {"alg": "RS256", "kid": "k1"},
        {"sub": "u", "app": "my-app", "products": [], "exp": exp});

    expect(
        () => verifyLicence(good, jwks, expectedApp: "other", expectedSub: "u"),
        throwsA(isA<IapError>()));
    expect(
        () => verifyLicence(good, jwks,
            expectedApp: "my-app", expectedSub: "someone-else"),
        throwsA(isA<IapError>()));

    final tampered = "${good.substring(0, good.length - 4)}AAAA";
    expect(
        () => verifyLicence(tampered, jwks,
            expectedApp: "my-app", expectedSub: "u"),
        throwsA(isA<IapError>()));
  });

  test("rejects an expired licence", () {
    final pair = _genKey(3);
    final pub = pair.publicKey as RSAPublicKey;
    final priv = pair.privateKey as RSAPrivateKey;
    final jwks = {
      "keys": [
        {
          "kty": "RSA",
          "kid": "k1",
          "alg": "RS256",
          "n": _b64uBig(pub.modulus!),
          "e": _b64uBig(pub.exponent!)
        }
      ]
    };

    final past = DateTime.now()
            .toUtc()
            .subtract(const Duration(hours: 1))
            .millisecondsSinceEpoch ~/
        1000;
    final token = _signJwt(priv, {"alg": "RS256", "kid": "k1"},
        {"sub": "u", "app": "my-app", "products": [], "exp": past});

    expect(
        () =>
            verifyLicence(token, jwks, expectedApp: "my-app", expectedSub: "u"),
        throwsA(predicate((e) => e is IapError && e.code == "expired")));
  });
}