Implementing Refresh Tokens
Develop a strategy for issuing and managing refresh tokens to securely extend user sessions without frequent re-authentication.
Implementing Refresh Tokens is a free Spring Security 6 & JWT Authentication lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Security 6 & JWT Authentication learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Short-Lived Access Tokens?
In modern security, Access Tokens (like JWTs) are typically designed to be short-lived. This means they expire quickly, often within minutes or a few hours.
Why? If an access token is stolen, its short lifespan limits the time an attacker can use it to impersonate a user. This reduces the window of vulnerability.
The User Experience Challenge
While short-lived access tokens are great for security, they can create a poor user experience. Imagine needing to log in every 15 minutes because your access token expired!
Users expect to stay logged in for extended periods without constant re-authentication. This is where Refresh Tokens come to the rescue.
Introducing Refresh Tokens
A Refresh Token is a special, long-lived token issued alongside the short-lived access token during a user's initial login.
- It's not used to access resources directly.
- Its sole purpose is to obtain a new, valid access token once the current one expires.
- They typically have a much longer expiry (days, weeks, or even months).
The Refresh Token Flow
Here's how refresh tokens maintain user sessions securely:
- Login: User authenticates, receives both an Access Token and a Refresh Token.
- Access: User uses the access token for API requests.
- Expiration: When the access token expires, API requests fail.
- Refresh: The client sends the refresh token to a special endpoint to get a new access token.
- Continue: If the refresh token is valid, a new access token is issued, and the user continues without re-login.
Generating Refresh Tokens
Refresh tokens are often also JWTs, but with different claims and a much longer expiration time. They might include a 'type': 'refresh' claim to distinguish them from access tokens.
Here's a simplified example of how a JWT (acting as a refresh token) could be generated with a long expiry:
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.security.Keys;
import java.security.Key;
import java.util.Date;
import java.util.concurrent.TimeUnit;
public class RefreshTokenGenerator {
private static final Key SECRET_KEY = Keys.secretKeyFor(SignatureAlgorithm.HS256);
public static String generateRefreshToken(String username) {
long nowMillis = System.currentTimeMillis();
Date now = new Date(nowMillis);
// Refresh token valid for 7 days
long expiryMillis = nowMillis + TimeUnit.DAYS.toMillis(7);
Date expiry = new Date(expiryMillis);
return Jwts.builder()
.setSubject(username)
.claim("token_type", "refresh") // Custom claim
.setIssuedAt(now)
.setExpiration(expiry)
.signWith(SECRET_KEY)
.compact();
}
public static void main(String[] args) {
String user = "coddykit_user";
String refreshToken = generateRefreshToken(user);
System.out.println("Generated Refresh Token for " + user + ":");
System.out.println(refreshToken);
}
}Secure Client-Side Storage
Where should the client store the refresh token? This is critical for security:
- HTTP-only Cookies: For web applications, this is the most secure option. The browser sends them automatically, and JavaScript cannot access them, preventing XSS attacks.
- Secure Storage: For mobile apps, platform-specific secure storage (e.g., iOS Keychain, Android Keystore) should be used.
Never store refresh tokens in Local Storage! It's vulnerable to XSS.
Server-Side Management
For enhanced security and control, refresh tokens are often managed on the server-side as well:
- Database Storage: Store refresh tokens (or their hashes) in a database, linked to the user.
- Revocation: This allows the server to invalidate a refresh token immediately (e.g., if a user logs out, changes password, or a token is suspected to be compromised).
- One-Time Use: Some implementations make refresh tokens single-use, issuing a new one with each refresh request.
The Refresh Endpoint
Your Spring Boot application needs a dedicated API endpoint (e.g., /api/auth/refresh) that clients can call to exchange a valid refresh token for a new access token.
This endpoint should:
- Receive the refresh token from the client.
- Validate the refresh token's signature, claims, and expiry.
- Verify it against server-side storage (if applicable).
- If valid, generate and return a new access token (and potentially a new refresh token).
Refresh Endpoint Logic (Snippet)
Here's a conceptual snippet of a Spring controller method that handles a refresh request. Note that `isRunnable` is false as this is part of a larger Spring application context.
@RestController
@RequestMapping("/api/auth")
public class AuthController {
@Autowired
private JwtService jwtService;
@Autowired
private RefreshTokenService refreshTokenService;
@PostMapping("/refresh")
public ResponseEntity<TokenResponse> refreshAccessToken(@RequestBody RefreshRequest refreshRequest) {
String oldRefreshToken = refreshRequest.getRefreshToken();
// 1. Validate the old refresh token
if (!jwtService.validateToken(oldRefreshToken) || !refreshTokenService.isValidRefreshToken(oldRefreshToken)) {
return ResponseEntity.status(HttpStatus.UNAUTHORIZED).build();
}
String username = jwtService.extractUsername(oldRefreshToken);
// 2. Generate new access token
String newAccessToken = jwtService.generateAccessToken(username);
// 3. (Optional) Generate a new refresh token and invalidate the old one
String newRefreshToken = refreshTokenService.rotateRefreshToken(oldRefreshToken, username);
return ResponseEntity.ok(new TokenResponse(newAccessToken, newRefreshToken));
}
}Refresh Token Check
Which of the following are secure practices for managing refresh tokens?
Recap: Secure Sessions with Refresh Tokens
You've learned how Refresh Tokens are crucial for balancing strong security with a great user experience in applications using short-lived access tokens.
- They allow users to remain authenticated for longer periods.
- Secure storage (HTTP-only cookies, secure mobile storage) is vital.
- Server-side management enables revocation and token rotation for enhanced security.
This mechanism is fundamental for robust, modern authentication systems.
Frequently asked questions
Is the “Implementing Refresh Tokens” lesson free?
Yes — the full text of “Implementing Refresh Tokens” is free to read here on the web, and the Spring Security 6 & JWT Authentication course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Security 6 & JWT Authentication course, upgrade to CoddyKit PRO.
What will I learn in “Implementing Refresh Tokens”?
Develop a strategy for issuing and managing refresh tokens to securely extend user sessions without frequent re-authentication. You practise Spring Security 6 & JWT Authentication with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Spring Security 6 & JWT Authentication?
No prior experience is required. Spring Security 6 & JWT Authentication on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Implementing Refresh Tokens” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Spring Security 6 & JWT Authentication lesson?
Yes. Every Spring Security 6 & JWT Authentication lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Implementing Refresh Tokens
- JWT Token Revocation Strategies
- Secure Token Storage Practices
- Rotating Signing Keys and Key Management