Mastering JWT Tokens: From Basics to Best Practices
JSON Web Tokens (JWT) have become a cornerstone of modern web authentication and API authorization. They're compact, URL-safe and easy to work with, making them a popular choice for developers building secure web and mobile applications.
In this guide, we will take you on a journey from the basics of JWTs to advanced use cases and best practices.
Table of Contents
- What is a JWT Token?
- JWT Structure Explained
- Why Use JWTs?
- How JWT Authentication Works
- Common Use Cases
- JWT Implementation
- JWT Security Best Practices
What is a JWT Token?
JWT (JSON Web Token) is a compact, URL-safe token used to securely transmit claims between two parties. It's digitally signed, allowing systems to verify authenticity without relying on a centralized session store. JWTs are widely used for authentication, authorization and secure information exchange in modern web applications.
JWT Structure
A JWT consists of three base64-encoded parts separated by dots (.)
<Header>.<Payload>.<Signature>
1. Header
Typically consists of two parts: the type of token and the signing algorithm
{ "alg": "HS256", "typ": "JWT" }
2. Payload
Contains the claims. Claims are statements about an entity (typically, the user) and additional metadata.
{ "sub": "1234567890", "name": "John Doe", "admin": true, "exp": 1717040000 }
Claims can be registered, public, or private.
3. Signature
Used to verify the token was not altered. It's created by combining the encoded header, payload, a secret key and the algorithm specified. The JWT signature is calculated like this
HMACSHA256( base64UrlEncode(header) + "." + base64UrlEncode(payload), secret)
Then the resulting JWT looks like
JWT = base64urlEncode(header) + "." + base64urlEncode(payload) + "." + base64urlEncode(signature)
Why Use JWTs?
JWTs offer several advantages
- ✅ Stateless Authentication
- ✅ Scalability
- ✅ Compact and Portable
- ✅ Cross-domain support
- ✅ Secure Information Exchange
How JWT Authentication Works
Here’s a step-by-step flow of JWT-based authentication
🔐 Step 1: Login Request
User provides credentials (e.g., username/password).
🔑 Step 2: Token Issued
Server verifies credentials and issues a signed JWT.
📦 Step 3: Token Stored Client-side
Token is usually stored in localStorage or cookies.
🔄 Step 4: Token Sent with Requests
Client sends the token in the Authorization header
Authorization: Bearer <token>
✅ Step 5: Token Verified
Server validates the token's signature and expiration before granting access.
Common Use Cases
Authentication (Login Sessions)
- Use Case: After a user logs in successfully, the server creates a JWT and sends it to the client.
- Client stores it: Usually in localStorage or cookies.
- Sent on each request: Attached as an Authorization: Bearer <token> header.
- Benefits: Stateless authentication (no need to store session in the backend).
Authorization
- Use Case: Determine user access to specific resources (e.g., admin-only dashboards, role-based permissions).
Information Exchange
- Use Case: Securely transmit user or session information between parties.
- Example: Microservices can pass user context with JWTs for API-to-API communication.
Single Sign-On (SSO)
- Use Case: JWTs are ideal for SSO implementations because they can securely carry user identity across different domains or services.
- Example: Authenticate once in Service A → Access Services B, C, D using same JWT.
Stateless APIs (Token-based Authentication)
- Use Case: RESTful APIs use JWTs to manage authentication without requiring a session store.
- JWTs fit perfectly into HTTP headers and mobile APIs.
OAuth 2.0 / OpenID Connect
- Use Case: JWTs (often in the form of ID tokens or access tokens) are standard in OAuth and OpenID Connect flows.
- Example: Google, Facebook, Microsoft use JWT-based ID tokens for login.
Refresh Tokens
- Use Case: Combine short-lived access tokens with long-lived refresh tokens.
- JWT for access: Keeps user logged in with minimal security risk.
Cross-Service Communication in Microservices
- Use Case: Pass identity/context between microservices using JWTs.
- Benefits: No central auth server needed to re-check credentials.
Serverless & Edge Architectures
- Use Case: Stateless nature of JWTs makes them perfect for serverless apps (e.g., AWS Lambda, Cloudflare Workers).
Secure WebSocket Authentication
- Use Case: Use JWT in the initial WebSocket handshake to authenticate clients.
JWT Implementation
A complete, structured guide to implementing JWT authentication in Java (Spring Boot). Full step by step guide with code & explanation
👉 Read a full guide how to Implement JWT in Java (Step-by-Step)JWT Security Best Practices
- Use HTTPS Always : Always send tokens over HTTPS to prevent man-in-the-middle attacks.
- Set Expiry (exp) : Always define an expiration (exp) for your JWTs tokens, should never live forever. Short-lived tokens reduce risk. For longer user sessions, pair them with a refresh token system to maintain both security and usability.
- Keep JWT Payload Minimal : Only include essential information in the JWT payload. Avoid putting sensitive data like passwords, secrets or personal details
- Rotate Secrets : Change your signing secret/key periodically.
- Implement Refresh Tokens Securely : Use short-lived access tokens for better security and long-lived refresh tokens to maintain user sessions. Store refresh tokens securely using HTTP-only cookies and ensure they are revoked on logout or when suspicious activity is detected.
- Never Store JWTs in LocalStorage : Avoid storing JWTs in LocalStorage, as it's susceptible to XSS attacks. Instead, use HTTP-only, Secure cookies to store tokens safely and protect user data from client-side threats.
- Use Strong Signing Algorithms : Always sign JWTs using secure algorithms like HS256 or RS256. Avoid using the none algorithm, which can allow unsigned tokens and pose serious security risks.
- Revoke Tokens on Logout or Breach : Since JWTs are stateless, revoking them isn’t straightforward. To handle this, consider using a blacklist or tracking token IDs (jti) so you can manually revoke tokens when a user logs out or if there’s any suspicious activity. It's an extra step, but crucial for maintaining security.
- Prevent Token Leakage in URLs : Avoid sending JWTs in query parameters like ?token=abc123. They are easily exposed through browser history, server logs or third-party analytics. Instead, always pass tokens securely using the Authorization header.
Conclusion
JWTs are a powerful way to handle authentication and authorization in modern web applications. When used correctly, they can make your app more scalable, secure, and flexible.
Whether you're building a login system, securing APIs, or managing microservices communication, JWTs can be your go-to choice.