Part 5: JWT token Java | User Management Service Java GRPC

Public and Private Keys for JWT token
- Generate Public and Private Keys
- Store Public and Private keys in the Resources folder
Java Dependency for JWT token generation
Public and Private Key Generator/Supplier for JWT Library
Java JWT token generator
Sample Token
References

In today’s world of microservice deployment, architecture is widely used and if you want to perform authentication and authorization across multiple services then JSON Web Token (JWT) is widely used. we will also create JWT when a user does a successful authentication. Let’s learn to create the JWT token in our User Management service.

Public and Private Keys for JWT token

For JWT token generation you need to choose an algorithm that will help you to sign your JWT token. Symmetric algorithms and Asymmetric algorithms are available like HMAC, and RSA256. In a symmetric algorithm, a single key is used to both create and verify the token. In an asymmetric algorithm, we have two keys one for signing the token and another for verifying the token.

Private Key: This key is used for signing or creating the token
Public Key: This key is used for verifying the token

we will be using the Asymmetric algorithm RSA256 in our user management service.

Generate Public and Private Keys

There are multiple ways to generate the private and public keys. we will be using the online website. visit the website for generating the keys

https://acte.ltd/utils/openssl

Online website to generate the JWT public and private keys

You need to select the options from the list and then click on Generate Keys

Algorithm: RSA
size: 2048
Leave the passphrase empty

After clicking the GENERATE KEYS button click on the PKCS8 format. You will see the public and private keys at the bottom of the screen

Store Public and Private keys in the Resources folder

Create the resources folder and then create two files

Store public and private JWT keys in resources folder.

private_key.pem
public_key.pem

Copy the public key and private key from the website which we generated earlier and then save them in appropriate files.

The private key that we are using is

The public key that we are using is

Java Dependency for JWT token generation

we need a library to generate the Java JWT token. we will be using auth0 java-jwt library for our project. let’s add the below library in the dependencies of your build.gradle file

  implementation 'com.auth0:java-jwt:4.4.0'

Public and Private Key Generator/Supplier for JWT Library

we have downloaded the public and private keys and stored them in a file. Now we want to read the keys from the file and then supply it to the JWT library. Create a new folder service and add the JWTKeyGenerator.java file

JWTKeyGenerator.java class for JWT key supplier

Put the below content in JWTKeyGenerator.java class

package user.management.system.grpc.service;

import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

import user.management.system.grpc.exception.Exception5XX;

public class JWTKeyGenerator {
   

    public  RSAPublicKey getPublicKey() throws Exception5XX {
        
        try {
            String publicKeyContent = new String(Files.readAllBytes(Paths.get(ClassLoader.getSystemResource("public_key.pem").toURI())),Charset.defaultCharset());
            publicKeyContent = publicKeyContent.replaceAll("\\n", "").replace("-----BEGIN PUBLIC KEY-----", "").replace("-----END PUBLIC KEY-----", "");
            byte[] encoded = Base64.getDecoder().decode(publicKeyContent);
            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
            X509EncodedKeySpec keySpec = new X509EncodedKeySpec(encoded);
            return (RSAPublicKey) keyFactory.generatePublic(keySpec);
        } catch (Exception e) {
            e.printStackTrace();
            throw new Exception5XX("10000", "public key", "public key generation error");
        } 
       
        
    }

    public  RSAPrivateKey getPrivateKey() throws Exception5XX {
        try {
            String privateKeyContent = new String(Files.readAllBytes(Paths.get(ClassLoader.getSystemResource("private_key.pem").toURI())),Charset.defaultCharset());
            privateKeyContent = privateKeyContent.replaceAll("\\n", "").replace("-----BEGIN PRIVATE KEY-----", "").replace("-----END PRIVATE KEY-----", "");
            privateKeyContent = privateKeyContent.replaceAll("\\s", "");
            byte[] encoded = Base64.getDecoder().decode(privateKeyContent);

            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
            PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
            return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
        } catch (Exception e) {
            e.printStackTrace();
            throw new Exception5XX("10000", "private key", "private key generation error");
        }
    }
}

Public Methods
- getPublicKey
  - Reads the public key from public_key.pem file of the resources folder and return the RSAPublicKey object
- getPrivateKey
  - Reads the private key from private_key.pem file of the resources folder and return the RSAPrivateKey object

Java JWT token generator

Now we have the public and private key suppliers from the JWTKeyGenerator class. Let’s create the JWT token. Create a new file JWTService.java in the service folder

Put the below content in the JWTService.java

package user.management.system.grpc.service;

import java.util.Date;
import java.util.concurrent.TimeUnit;

import com.auth0.jwt.JWT;
import com.auth0.jwt.algorithms.Algorithm;

import user.management.system.grpc.exception.Exception5XX;



public class JWTService {
    JWTKeyGenerator jwtKeyGenerator = new JWTKeyGenerator();
    public String generateToken(String firstName, String email, String lastName, int id) throws Exception5XX {
       
        Algorithm algorithm = Algorithm.RSA256(jwtKeyGenerator.getPublicKey(), jwtKeyGenerator.getPrivateKey());
        String token = JWT.create()
                .withIssuer("user-managment-system-grpc")
                .withClaim("firstName", firstName)
                .withClaim("lastName", lastName)
                .withClaim("email", email)
                .withClaim("id", id)
                .withExpiresAt(new Date(System.currentTimeMillis() + TimeUnit.MINUTES.toMillis(5)))
                .sign(algorithm);
               
        return token;
    }
    
}

Instance Variables
- jwtKeyGenerator
  - This holds the instance of JWTKeyGenerator that is supplied through the constructor
Public Methods
- generateToken
  - Uses the RSA256 Algorithm and used the private and public key
  - Claims are supplied which is nothing but key-value pair that will be present in the JWT token
  - The token is signed with the algorithm and returned

Sample Token

The sample token which will be generated later on will be

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJ1c2VyLW1hbmFnbWVudC1zeXN0ZW0tZ3JwYyIsImZpcnN0TmFtZSI6InJhaiIsImxhc3ROYW1lIjoicmFuamFuIiwiZW1haWwiOiJhYmNAZ21haWwuY29tIiwiaWQiOjEyLCJleHAiOjE3MTQyODExNzd9.YJd9HFrg7k9FNzF-gMALVnI0e3eteGCFnTRE3E-OHyj4p1HfQasm46FyQZ4aXvmuxJDk-k9Viao9ZLvSRa73qENk2o6ewBBmjFrtYfA4ZIyfdiieCyvpxXcu4aEOpYOuBcXyrNm0Gq7_5erA5lglB0gbxBkUw9ig8IZmICA-JkcEGdPEVREyYv9bEu2lm0-_MC3IEbqCHBBNSy0Wz741O8vw4cYtLRKEjzHyWgl8LmrDNG-hdslqYmP8fQ8b5yF8pmeKzegfhI7i5dIZInCNJwNtq3n1egzRitVjl6txSRpdPFG8FqfGpbmZdJNfUfwfAAa2Q_bYJpbEnIiWGJjdkw

This is the process to generate a JWT token in Java

Previous: Part 4: Create User in User Management Service GRPC Java

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Part 5: JWT token Java | User Management Service Java GRPC

Public and Private Keys for JWT token

Generate Public and Private Keys

Store Public and Private keys in the Resources folder

Java Dependency for JWT token generation

Public and Private Key Generator/Supplier for JWT Library

Java JWT token generator

Sample Token

References

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