Java

Validate the at_hash Claim of an ID Token

See more JSON Web Token (JWT) Examples

Demonstrates how to hash an access token to compare it with the at_hash claim of an ID token. Chilkat2 Java

import com.chilkatsoft.chilkat2.BinData;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Crypt2;
import com.chilkatsoft.chilkat2.JsonObject;
import com.chilkatsoft.chilkat2.Jwt;

public class ChilkatExample {

    public static void main(String[] args) {
        // This example requires the Chilkat API to have been previously unlocked.
        // See Global Unlock Sample for sample code.

        // This example uses a Google access_token + id_token that looks like this:

        //  {
        //   "access_token": "ya29.a0...0f",
        //   "expires_in": 3599,
        //   "scope": "openid https://www.googleapis.com/auth/userinfo.email",
        //   "token_type": "Bearer",
        //   "id_token": "eyJhb...o5nQ"
        // }

        JsonObject jsonToken = new JsonObject();
        try {
            jsonToken.loadFile("qa_data/tokens/google_sample_id_token.json");
        } catch (ChilkatException e) {
            System.out.println("Failed to load the JSON file...");
            return;
        }

        // Use Chilkat's JWT API to examine the id_token..
        Jwt jwt = new Jwt();
        String idToken = jsonToken.stringOf("id_token");

        // Extract the JOSE header..
        String jose = jwt.getHeader(idToken);

        JsonObject jsonHeader = new JsonObject();
        jsonHeader.load(jose);
        jsonHeader.setEmitCompact(false);
        System.out.println(jsonHeader.emit());

        // The JOSE header looks like this:

        // {
        //   "alg": "RS256",
        //   "kid": "e8799db06287515556213c80acbcfd022fb302a9",
        //   "typ": "JWT"
        // }

        String claims = jwt.getPayload(idToken);

        JsonObject jsonClaims = new JsonObject();
        jsonClaims.load(claims);
        jsonClaims.setEmitCompact(false);
        System.out.println(jsonClaims.emit());

        // The claims look like this:

        // {
        //   "iss": "https://accounts.google.com",
        //   "azp": "258999997753-5ni8lu5f15r7mno97d82f5lir9i9f6i1.apps.googleusercontent.com",
        //   "aud": "258999997753-5ni8lu5f15r7mno97d82f5lir9i9f6i1.apps.googleusercontent.com",
        //   "sub": "111787341816486547572",
        //   "email": "somebody@gmail.com",
        //   "email_verified": true,
        //   "at_hash": "HYJZImlW3mUK-UfjRfXjKw",
        //   "iat": 1615315968,
        //   "exp": 1615319568
        // }

        // The at_hash is the Access Token hash value. Its value is the base64url encoding of the
        // left-most half of the hash of the octets of the ASCII representation of the access_token value,
        // where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the
        // ID Token's JOSE Header. For instance, if the alg is RS256, hash the access_token value with SHA-256,
        // then take the left-most 128 bits and base64url encode them. The at_hash value is a case sensitive string.

        String token_to_hash = jsonToken.stringOf("access_token");
        String token_hash_expected = jsonClaims.stringOf("at_hash");

        // Step 1. hashes the access token using SHA-256 (Google uses `RS256` as the ID Token `alg`).
        Crypt2 crypt = new Crypt2();
        BinData bdHash = new BinData();

        crypt.setHashAlgorithm("sha256");
        // This encoding mode must match the encoding mode passed in the 2nd arg to AppendEncoded.
        // The encoding mode can be anything, as long as they are the same in both places.
        crypt.setEncodingMode("hex");

        bdHash.appendEncoded(crypt.hashStringENC(token_to_hash), "hex");
        int sz = bdHash.getNumBytes();

        String token_hash_computed = bdHash.getEncodedChunk(0, sz / 2, "base64url");

        // If the hashes are identical, then the access_token as issued for the given id_token.
        System.out.println("token_hash_expected: " + token_hash_expected);
        System.out.println("token_hash_computed: " + token_hash_computed);
    }
}