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Java JWT Validation Example

⚠️ Important Notice: This is a basic example for demonstration purposes only. For production use, please research and implement best practices specific to your software stack, security requirements, and deployment environment. Always follow your organization's security guidelines and consider using established JWT libraries and frameworks.

📝 Note: This example demonstrates JWKS downloading and file caching for educational purposes. In production environments, you may choose to implement JWKS key management differently based on your infrastructure - such as using configuration management, environment variables, or your preferred caching strategy.

This example demonstrates how to validate Rokt JWT tokens using Java.

Prerequisites​

Add the following dependencies to your pom.xml:

<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-api</artifactId>
    <version>0.11.5</version>
</dependency>
<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-impl</artifactId>
    <version>0.11.5</version>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt-jackson</artifactId>
    <version>0.11.5</version>
    <scope>runtime</scope>
</dependency>

Complete Example​

package com.rokt;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import java.math.BigInteger;
import java.security.Key;
import java.security.KeyFactory;
import java.security.spec.ECPublicKeySpec;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.util.Base64;
import java.util.Date;

public class RoktJwtValidator {
    
    // Copy the test token from the Overview page
    private static final String SAMPLE_JWT_TOKEN = "PASTE_TEST_TOKEN_HERE";
    
    // JWKS endpoint URL
    private static final String JWKS_URL = "https://public-api.rokt.com/.well-known/jwks.json";
    
    public static void main(String[] args) {
        try {
            System.out.println("=== Java JWT Validator ===");
            System.out.println("Token: " + SAMPLE_JWT_TOKEN.substring(0, 50) + "...");
            System.out.println("JWKS URL: " + JWKS_URL);
            System.out.println();
            
            // Download and cache JWKS
            String jwksJson = downloadAndCacheJWKS(JWKS_URL, JWKS_CACHE_FILE);
            System.out.println("JWKS downloaded and cached successfully");
            
            // Extract public key coordinates from JWKS
            String[] coordinates = extractKeyCoordinates(jwksJson);
            String xCoordinate = coordinates[0];
            String yCoordinate = coordinates[1];
            
            // Create ECDSA public key from JWK coordinates
            Key publicKey = createECDSAPublicKey(xCoordinate, yCoordinate);
            
            // Validate JWT token
            Claims claims = validateJWT(SAMPLE_JWT_TOKEN, publicKey);
            
            System.out.println("✅ Token validation successful!");
            System.out.println("Campaign ID: " + claims.get("cid"));
            System.out.println("Creative ID: " + claims.get("crid"));
            System.out.println("RCLID: " + claims.get("rclid"));
            System.out.println("Issued At: " + new Date(claims.getIssuedAt().getTime()) + " UTC");"
            
        } catch (Exception e) {
            System.err.println("❌ Token validation failed: " + e.getMessage());
            e.printStackTrace();
        }
    }
    
    private static Claims validateJWT(String token, Key publicKey) {
        return Jwts.parserBuilder()
                .setSigningKey(publicKey)
                .setAllowedClockSkewSeconds(3600) // Allow 1 hour clock skew for demo - using sample token
                .build()
                .parseClaimsJws(token)
                .getBody();
    }
    
    private static Key createECDSAPublicKey(String xCoordinate, String yCoordinate) throws Exception {
        // Decode base64url encoded coordinates
        byte[] xBytes = Base64.getUrlDecoder().decode(xCoordinate);
        byte[] yBytes = Base64.getUrlDecoder().decode(yCoordinate);
        
        // Convert to BigInteger
        BigInteger x = new BigInteger(1, xBytes);
        BigInteger y = new BigInteger(1, yBytes);
        
        // Use standard P-256 curve from AlgorithmParameters
        java.security.AlgorithmParameters parameters = java.security.AlgorithmParameters.getInstance("EC");
        parameters.init(new java.security.spec.ECGenParameterSpec("secp256r1"));
        ECParameterSpec ecParameterSpec = parameters.getParameterSpec(ECParameterSpec.class);
        
        // Create ECDSA public key spec
        ECPublicKeySpec spec = new ECPublicKeySpec(
            new ECPoint(x, y),
            ecParameterSpec
        );
        
        // Generate public key
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        return keyFactory.generatePublic(spec);
    }
}

Input/Output Example​

Input​

  • JWT Token: Copy the test token from the Overview page
  • Public Key Source: https://public-api.rokt.com/.well-known/jwks.json

Output​

=== Java JWT Validator ===
Token: eyJhbGciOiJFUzI1NiIsImtpZCI6InJva3Qtc2lnbmluZy1rZX...
JWKS URL: https://public-api.rokt.com/.well-known/jwks.json

Downloading JWKS from: https://public-api.rokt.com/.well-known/jwks.json
JWKS cached to: jwks_cache.json
JWKS downloaded and cached successfully

✅ Token validation successful!
Campaign ID: 3436085368692408324
Creative ID: 3437732754935906308
RCLID: 7db958dbd232247a4a8285a34d22fe0f4e9affa463bf5ee54e26721ab0df0e23
Issued At: Wed Aug 20 15:10:01 AEST 2025 UTC

How to Run​

  1. Create a Maven project with pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.rokt</groupId>
    <artifactId>jwt-validator</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <properties>
        <maven.compiler.source>15</maven.compiler.source>
        <maven.compiler.target>15</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-api</artifactId>
            <version>0.11.5</version>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-impl</artifactId>
            <version>0.11.5</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-jackson</artifactId>
            <version>0.11.5</version>
            <scope>runtime</scope>
        </dependency>
    </dependencies>
</project>
  1. Save the code to src/main/java/com/rokt/RoktJwtValidator.java
  2. Run: mvn compile exec:java -Dexec.mainClass="com.rokt.RoktJwtValidator"

Using JAR files directly​

  1. Download JJWT JAR files
  2. Save the code to RoktJwtValidator.java
  3. Compile: javac -cp ".:jjwt-api-0.11.5.jar:jjwt-impl-0.11.5.jar:jjwt-jackson-0.11.5.jar" RoktJwtValidator.java
  4. Run: java -cp ".:jjwt-api-0.11.5.jar:jjwt-impl-0.11.5.jar:jjwt-jackson-0.11.5.jar" RoktJwtValidator

Notes​

  • The public key is retrieved from Rokt's JWKS endpoint

  • The example uses ECDSA-256 (ES256) algorithm for signature verification

  • Consider caching the public key for performance

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