IDToken Signature Verification

The WSO2 Identity Server is shipped with a signed ID Token. This is provided in order to address some security vulnerabilities in a typical production environment. This topic provides information about using this signed ID Token for signature verification.

The portions of each token are separated by the full stop. To see the exact JSON values, do a Base64 decode for <header>.<body>.

If the unsigned ID token contains only 2 portions:
It is in the following format: <header>.<body>
Sample of unsigned ID token
```
eyJhbGciOiJSUzI1NiJ9.eyJzdWIiOiJhbGljZSIsImlzcyI6Imh0dHBzOlwvXC9jMmlkLmNvbSIsImlhdCI6MTQxNjE1ODU0MX0 
```

If the signed ID token contains 3 portions:
It is in the following format: <header>.<body>.<signature>

Sample of signed ID token

eyJhbGciOiJSUzI1NiJ9.eyJzdWIiOiJhbGljZSIsImlzcyI6Imh0dHBzOlwvXC9jMmlkLmNvbSIsImlhdCI6MTQxNjE1ODU0MX0.iTf0eDBF-6-OlJwBNxCK3nqTUjwC71-KpqXVr21tlIQq4_ncoPODQxuxfzIEwl3Ko_Mkt030zJs-d36J4UCxVSU21hlMOscNbuVIgdnyWhVYzh_-v2SZGfye9GxAhKOWL-_xoZQCRF9fZ1j3dWleRqIcPBFHVeFseD_64PNemyg

Validating the ID token signature

The following code segment is a simple Java program that can be used to validate the ID token signature against the default wso2carbon.jks public key in WSO2 products.

package org.sample;

import java.io.InputStream;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.interfaces.RSAPublicKey;

import com.nimbusds.jose.JWSVerifier;
import com.nimbusds.jose.crypto.RSASSAVerifier;
import com.nimbusds.jwt.SignedJWT;

public class ValidateRSASignature {

    public static void main(String[] args) throws Exception {
        RSAPublicKey publicKey = null;
        InputStream file = ClassLoader
                .getSystemResourceAsStream("wso2carbon.jks");
        KeyStore keystore = KeyStore.getInstance(KeyStore.getDefaultType());
        keystore.load(file, "wso2carbon".toCharArray());

        String alias = "wso2carbon";

        // Get certificate of public key
        Certificate cert = keystore.getCertificate(alias);
        // Get public key
        publicKey = (RSAPublicKey) cert.getPublicKey();

        // Enter JWT String here
        String signedJWTAsString = "eyJhbGciOiJSUzI1NiJ9.eyJzdWIiOiJhbGljZSIsImlzcyI6Imh0d";

        SignedJWT signedJWT = SignedJWT.parse(signedJWTAsString);

        JWSVerifier verifier = new RSASSAVerifier(publicKey);

        if (signedJWT.verify(verifier)) {
            System.out.println("Signature is Valid");
        } else {
            System.out.println("Signature is NOT Valid");
        }
    }
}