火力基地| 使用第三方JWT库验证ID令牌

Question

Attempting to validate firebase id tokens using jjwt. Using GoogleCredential class to pull the private key. But I'm not sure if that's correct. Receiving an error: JWT signature does not match locally computed signature. Am I supposed to be using the private key here from service account json? Maybe I'm misunderstanding what ...setSigningKey(...) takes in.

@Service
public class FirebaseAuthVerifier implements AuthVerifier {

    private static final Logger logger = LoggerFactory.getLogger(FirebaseAuthVerifier.class);

    @Autowired
    private FirebaseProperties fbProps;

    public boolean verify(AuthToken token) throws GeneralSecurityException, IOException {
        // get google credential
        InputStream stream = new FileInputStream("src/main/resources/service-account.json");
        ByteArrayOutputStream streamCopy = new ByteArrayOutputStream();
        ByteStreams.copy(stream, streamCopy);
        stream.close();

        GoogleCredential gc = GoogleCredential.fromStream(
                new ByteArrayInputStream(streamCopy.toByteArray()),
                new NetHttpTransport(),
                GsonFactory.getDefaultInstance());

        try {
            Jwts.parser().setSigningKey(gc.getServiceAccountPrivateKey()).parse(token.getTokenId());
        } catch(Exception e) {
            // log
            logger.info("Firebase auth token verification error: ");
            logger.info(e.getMessage());
            // claims may have been tampered with
            return false;
        }

        return true;
    }

}

Answer 1

You're on the right lines! The key from the service account is used when creating JWTs to send to Google/Firebase. You really don't want to put that in your APK, as any malicious individual could steal it and use it to create ID tokens as you!

When you're validating a token from Firebase, you need to check Firebase's own keys - luckily, these are public! You can grab them from https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com - they rotate every few hours. If you look in that file you'll see it's a JSON dictionary, like this:

"8226146523a1b8894ba03ad525667b9475d393f5": "---CERT---",

The key in this is the kid field in the header of the ID token JWT - it corresponds to the key the token was signed with, meaning the cert that corresponds can be used to verify the signature.

Take a look at the (server side) docs for validating ID tokens for more.

Answer 2

Using custom jwt id token validation

@Service
public class FirebaseAuthVerifier implements AuthVerifier {

    private static final Logger logger = LoggerFactory.getLogger(FirebaseAuthVerifier.class);
    private static final String pubKeyUrl = "https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com";

    /**
     *
     * @param token
     * @return
     * @throws GeneralSecurityException
     * @throws IOException
     */
    public boolean verify(AuthToken token) throws GeneralSecurityException, IOException {
        // get public keys
        JsonObject publicKeys = getPublicKeysJson();

        // verify count
        int size = publicKeys.entrySet().size();
        int count = 0;

        // get json object as map
        // loop map of keys finding one that verifies
        for (Map.Entry<String, JsonElement> entry: publicKeys.entrySet()) {
            // log
            logger.info("attempting jwt id token validation with: ");

            try {
                // trying next key
                count++;

                // get public key
                PublicKey publicKey = getPublicKey(entry);

                // validate claim set
                Jwts.parser().setSigningKey(publicKey).parse(token.getTokenId());

                // success, we can return
                return true;
            } catch(Exception e) {
                // log
                logger.info("Firebase id token verification error: ");
                logger.info(e.getMessage());
                // claims may have been tampered with
                // if this is the last key, return false
                if (count == size) {
                    return false;
                }
            }
        }

        // no jwt exceptions
        return true;
    }

    /**
     *
     * @param entry
     * @return
     * @throws GeneralSecurityException
     */
    private PublicKey getPublicKey(Map.Entry<String, JsonElement> entry) throws GeneralSecurityException, IOException {
        String publicKeyPem = entry.getValue().getAsString()
                .replaceAll("-----BEGIN (.*)-----", "")
                .replaceAll("-----END (.*)----", "")
                .replaceAll("\r\n", "")
                .replaceAll("\n", "")
                .trim();

        logger.info(publicKeyPem);

        // generate x509 cert
        InputStream inputStream = new ByteArrayInputStream(entry.getValue().getAsString().getBytes("UTF-8"));
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        X509Certificate cert = (X509Certificate)cf.generateCertificate(inputStream);

        return cert.getPublicKey();
    }

    /**
     *
     * @return
     * @throws IOException
     */
    private JsonObject getPublicKeysJson() throws IOException {
        // get public keys
        URI uri = URI.create(pubKeyUrl);
        GenericUrl url = new GenericUrl(uri);
        HttpTransport http = new NetHttpTransport();
        HttpResponse response = http.createRequestFactory().buildGetRequest(url).execute();

        // store json from request
        String json = response.parseAsString();
        // disconnect
        response.disconnect();

        // parse json to object
        JsonObject jsonObject = new JsonParser().parse(json).getAsJsonObject();

        return jsonObject;
    }

}