Author: Vinay

In my previous article , I talked about JWT introduction and how it works. There are multiple libraries by which you can implement JWT in Java.

1. Java JWT: JSON Web Token for Java and Android

Installation

Use your favorite Maven-compatible build tool to pull the dependency (and its transitive dependencies) from Maven Central:

Maven:

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt</artifactId>
    <version>0.6.0</version>
</dependency>



Gradle:


dependencies {
    compile 'io.jsonwebtoken:jjwt:0.6.0'
}

Note: JJWT depends on Jackson 2.x. If you’re already using an older version of Jackson in your app, read this

Usage

Most complexity is hidden behind a convenient and readable builder-based fluent interface, great for relying on IDE auto-completion to write code quickly. Here’s an example:

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.impl.crypto.MacProvider;
import java.security.Key;

// We need a signing key, so we'll create one just for this example. Usually
// the key would be read from your application configuration instead.
Key key = MacProvider.generateKey();

String s = Jwts.builder().setSubject("Joe").signWith(SignatureAlgorithm.HS512, key).compact();
How easy was that!?

Now let's verify the JWT (you should always discard JWTs that don't match an expected signature):

assert Jwts.parser().setSigningKey(key).parseClaimsJws(s).getBody().getSubject().equals("Joe");
You have to love one-line code snippets!

But what if signature validation failed? You can catch SignatureException and react accordingly:

try {

    Jwts.parser().setSigningKey(key).parseClaimsJws(compactJwt);

    //OK, we can trust this JWT

} catch (SignatureException e) {

    //don't trust the JWT!
}

2. Using Nimbus Jose + JWT

The most popular and robust Java library for JSON Web Tokens (JWT)
Supports all standard signature (JWS) and encryption (JWE) algorithms
Open source Apache 2.0 licence

Features –

– Signed / encrypted tokens, such as bearer access tokens in OAuth 2.0 or OpenID Connect identity tokens;
– Self-contained API keys, with optional revocation;
– Protecting content and messages;
– Authenticating clients and web API requests.

Use in Java

// Create an HMAC-protected JWS object with some payload
JWSObject jwsObject = new JWSObject(new JWSHeader(JWSAlgorithm.HS256),
                                    new Payload("Hello world!"));

// We need a 256-bit key for HS256 which must be pre-shared
byte[] sharedKey = new byte[32];
new SecureRandom().nextBytes(sharedKey);

// Apply the HMAC to the JWS object
jwsObject.sign(new MACSigner(sharedKey));

// Output to URL-safe format
jwsObject.serialize(); 

Maven configuration

Maven
For Java 7+ :

<dependency>
    <groupId>com.nimbusds</groupId>
    <artifactId>nimbus-jose-jwt</artifactId>
    <version>4.11.2</version>
</dependency>

3. JSON token library – It depend on Google Guava.The library is in fact used by Google Wallet.

Here is how to create a jwt, and to verify it and deserialize it:

Maven –

<dependency>
    <groupId>com.googlecode.jsontoken</groupId>
    <artifactId>jsontoken</artifactId>
    <version>1.0</version>
</dependency>
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>18.0</version>
</dependency>

and Java implementation –

import java.security.InvalidKeyException;
import java.security.SignatureException;
import java.util.Calendar;
import java.util.List;

import net.oauth.jsontoken.JsonToken;
import net.oauth.jsontoken.JsonTokenParser;
import net.oauth.jsontoken.crypto.HmacSHA256Signer;
import net.oauth.jsontoken.crypto.HmacSHA256Verifier;
import net.oauth.jsontoken.crypto.SignatureAlgorithm;
import net.oauth.jsontoken.crypto.Verifier;
import net.oauth.jsontoken.discovery.VerifierProvider;
import net.oauth.jsontoken.discovery.VerifierProviders;

import org.apache.commons.lang3.StringUtils;
import org.bson.types.ObjectId;
import org.joda.time.DateTime;

import com.google.common.collect.Lists;
import com.google.gson.JsonObject;


/**
 * Provides static methods for creating and verifying access tokens and such. 
 * @author davidm
 *
 */
public class AuthHelper {

    private static final String AUDIENCE = "NotReallyImportant";

    private static final String ISSUER = "YourCompanyOrAppNameHere";

    private static final String SIGNING_KEY = "[email protected]^($%*$%";

    /**
     * Creates a json web token which is a digitally signed token that contains a payload (e.g. userId to identify 
     * the user). The signing key is secret. That ensures that the token is authentic and has not been modified.
     * Using a jwt eliminates the need to store authentication session information in a database.
     * @param userId
     * @param durationDays
     * @return
     */
    public static String createJsonWebToken(String userId, Long durationDays)    {
        //Current time and signing algorithm
        Calendar cal = Calendar.getInstance();
        HmacSHA256Signer signer;
        try {
            signer = new HmacSHA256Signer(ISSUER, null, SIGNING_KEY.getBytes());
        } catch (InvalidKeyException e) {
            throw new RuntimeException(e);
        }

        //Configure JSON token
        JsonToken token = new net.oauth.jsontoken.JsonToken(signer);
        token.setAudience(AUDIENCE);
        token.setIssuedAt(new org.joda.time.Instant(cal.getTimeInMillis()));
        token.setExpiration(new org.joda.time.Instant(cal.getTimeInMillis() + 1000L * 60L * 60L * 24L * durationDays));

        //Configure request object, which provides information of the item
        JsonObject request = new JsonObject();
        request.addProperty("userId", userId);

        JsonObject payload = token.getPayloadAsJsonObject();
        payload.add("info", request);

        try {
            return token.serializeAndSign();
        } catch (SignatureException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Verifies a json web token's validity and extracts the user id and other information from it. 
     * @param token
     * @return
     * @throws SignatureException
     * @throws InvalidKeyException
     */
    public static TokenInfo verifyToken(String token)  
    {
        try {
            final Verifier hmacVerifier = new HmacSHA256Verifier(SIGNING_KEY.getBytes());

            VerifierProvider hmacLocator = new VerifierProvider() {

                @Override
                public List<Verifier> findVerifier(String id, String key){
                    return Lists.newArrayList(hmacVerifier);
                }
            };
            VerifierProviders locators = new VerifierProviders();
            locators.setVerifierProvider(SignatureAlgorithm.HS256, hmacLocator);
            net.oauth.jsontoken.Checker checker = new net.oauth.jsontoken.Checker(){

                @Override
                public void check(JsonObject payload) throws SignatureException {
                    // don't throw - allow anything
                }

            };
            //Ignore Audience does not mean that the Signature is ignored
            JsonTokenParser parser = new JsonTokenParser(locators,
                    checker);
            JsonToken jt;
            try {
                jt = parser.verifyAndDeserialize(token);
            } catch (SignatureException e) {
                throw new RuntimeException(e);
            }
            JsonObject payload = jt.getPayloadAsJsonObject();
            TokenInfo t = new TokenInfo();
            String issuer = payload.getAsJsonPrimitive("iss").getAsString();
            String userIdString =  payload.getAsJsonObject("info").getAsJsonPrimitive("userId").getAsString();
            if (issuer.equals(ISSUER) && !StringUtils.isBlank(userIdString))
            {
                t.setUserId(new ObjectId(userIdString));
                t.setIssued(new DateTime(payload.getAsJsonPrimitive("iat").getAsLong()));
                t.setExpires(new DateTime(payload.getAsJsonPrimitive("exp").getAsLong()));
                return t;
            }
            else
            {
                return null;
            }
        } catch (InvalidKeyException e1) {
            throw new RuntimeException(e1);
        }
    }


}

public class TokenInfo {
    private ObjectId userId;
    private DateTime issued;
    private DateTime expires;
    public ObjectId getUserId() {
        return userId;
    }
    public void setUserId(ObjectId userId) {
        this.userId = userId;
    }
    public DateTime getIssued() {
        return issued;
    }
    public void setIssued(DateTime issued) {
        this.issued = issued;
    }
    public DateTime getExpires() {
        return expires;
    }
    public void setExpires(DateTime expires) {
        this.expires = expires;
    }
}

Happy API secure using JWT with Vinay

Reference
– https://github.com/jwtk/jjwt
– http://connect2id.com/products/nimbus-jose-jwt
– https://code.google.com/archive/p/jsontoken/