JWT structure (header, payload, signature) in Spring Boot - Mini Project: Build & Apply

JWT structure (header, payload, signature)

📖 Scenario: You are building a simple Spring Boot application that handles JSON Web Tokens (JWT). JWTs have three parts: header, payload, and signature. Understanding how to create and structure these parts is important for secure token handling.

🎯 Goal: Build a basic Spring Boot class that creates a JWT token by defining the header, payload, and signature parts as strings.

📋 What You'll Learn

Create a Map for the JWT header with algorithm and type

Create a Map for the JWT payload with user information

Create a String for the JWT signature placeholder

Combine these parts into a JWT token string separated by dots

💡 Why This Matters

🌍 Real World

JWTs are widely used for secure user authentication and data exchange in web applications.

💼 Career

Understanding JWT structure is essential for backend developers working with authentication and authorization in modern web services.

1

Create JWT header Map

Create a Map called header with these exact entries: "alg" set to "HS256" and "typ" set to "JWT".

Spring Boot

// Your code here

Need a hint?

Use a HashMap to store the header keys and values.

2

Create JWT payload Map

Create a Map called payload with these exact entries: "sub" set to "1234567890", "name" set to "John Doe", and "admin" set to true.

Spring Boot

Map header = new HashMap();
header.put("alg", "HS256");
header.put("typ", "JWT");
// Your code here

Need a hint?

Use a HashMap to store the payload keys and values. Note the value types: String and boolean.

3

Create JWT signature string

Create a String variable called signature and set it to the exact value "signature-placeholder".

Spring Boot

Map header = new HashMap();
header.put("alg", "HS256");
header.put("typ", "JWT");

Map payload = new HashMap();
payload.put("sub", "1234567890");
payload.put("name", "John Doe");
payload.put("admin", true);
// Your code here

Need a hint?

Just assign the exact string to the signature variable.

4

Combine header, payload, and signature into JWT token

Create a String variable called jwtToken that combines the strings "header", "payload", and "signature" separated by dots ("."). Use the exact code: jwtToken = "header.payload.signature";

Spring Boot

Map header = new HashMap();
header.put("alg", "HS256");
header.put("typ", "JWT");

Map payload = new HashMap();
payload.put("sub", "1234567890");
payload.put("name", "John Doe");
payload.put("admin", true);

String signature = "signature-placeholder";
// Your code here

Need a hint?

Combine the three parts as a single string separated by dots.