Refresh token pattern in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a refresh token in authentication?

A refresh token is used to get a new access token without asking the user to log in again. It helps keep the user logged in smoothly.

intermediate

How does the refresh token pattern improve security compared to long-lived access tokens?

It uses short-lived access tokens that expire quickly, reducing risk if stolen. The refresh token is stored securely and used to get new access tokens, limiting exposure.

intermediate

In Spring Boot, where is the refresh token usually stored on the client side?

The refresh token is often stored in an HttpOnly cookie to prevent JavaScript access and reduce cross-site scripting risks.

beginner

What happens if a refresh token is expired or invalid in the refresh token pattern?

The user must log in again because the system cannot issue a new access token without a valid refresh token.

intermediate

Describe the typical flow of the refresh token pattern in Spring Boot.

1. User logs in and receives access and refresh tokens.
2. Access token is used for API calls.
3. When access token expires, client sends refresh token to get a new access token.
4. Server validates refresh token and issues new access token.
5. If refresh token is invalid, user must log in again.

What is the main role of a refresh token?

A To encrypt API requests

B To replace the password

C To get a new access token without user login

D To store user profile data

A refresh token allows the client to request a new access token without making the user log in again.

Where should refresh tokens be stored on the client for better security in Spring Boot apps?

A Local storage

B HttpOnly cookie

C Session storage

D In the URL

HttpOnly cookies prevent JavaScript access, reducing risk of token theft via cross-site scripting.

What happens if the refresh token is expired when the client tries to get a new access token?

A The client must log in again

B The server issues a new refresh token automatically

C The access token is extended automatically

D The server ignores the request

An expired refresh token means the client cannot get a new access token and must ask the user to log in again.

Why use short-lived access tokens with refresh tokens?

A To limit damage if access token is stolen

B To reduce server load

C To improve user interface speed

D To store more user data

Short-lived access tokens reduce the time a stolen token can be used, improving security.

In the refresh token pattern, which token is sent with every API request?

A Refresh token

B Both tokens

C No token

D Access token

The access token is sent with API requests to authorize them; the refresh token is only used to get new access tokens.

Explain the refresh token pattern and why it is used in Spring Boot applications.

Think about how to keep users logged in safely without long-lasting tokens.

Describe the steps involved when a client uses a refresh token to get a new access token.

Focus on the communication between client and server during token renewal.

Practice

1.

What is the main purpose of using a refresh token in a Spring Boot authentication system?

easy

A. To encrypt user data in the database

B. To store user passwords securely

C. To log out users automatically after a timeout

D. To allow users to get a new access token without logging in again

Solution

1. Step 1: Understand the role of refresh tokens

   Refresh tokens are used to get new access tokens without asking the user to log in again.

2. Step 2: Compare options with this purpose

   Only To allow users to get a new access token without logging in again describes this purpose correctly; others describe unrelated functions.

3. Final Answer:

   To allow users to get a new access token without logging in again -> Option D

4. Quick Check:

   Refresh token purpose = renew access token [OK]

Hint: Refresh tokens renew access tokens without re-login [OK]

Common Mistakes:

• Confusing refresh token with password storage
• Thinking refresh token logs out users
• Assuming refresh token encrypts data

2.

Which of the following is the correct way to define a method in a Spring Boot controller to handle refresh token requests?

@PostMapping("/refresh")
public ResponseEntity<TokenResponse> refreshToken(@RequestBody RefreshRequest request) {
    // method body
}

easy

A. @GetMapping("/refresh") public TokenResponse refreshToken(@RequestBody RefreshRequest request)

B. @PostMapping("/refresh") public void refreshToken(String token)

C. @PostMapping("/refresh") public ResponseEntity<TokenResponse> refreshToken(@RequestBody RefreshRequest request)

D. @RequestMapping("/refresh") public String refreshToken()

Solution

1. Step 1: Check HTTP method and parameters

   The refresh token request should be a POST with a JSON body containing the refresh token.

2. Step 2: Match method signature

   @PostMapping("/refresh") public ResponseEntity<TokenResponse> refreshToken(@RequestBody RefreshRequest request) correctly uses @PostMapping, returns ResponseEntity<TokenResponse>, and accepts @RequestBody RefreshRequest.

3. Final Answer:

   @PostMapping("/refresh") public ResponseEntity<TokenResponse> refreshToken(@RequestBody RefreshRequest request) -> Option C

4. Quick Check:

   Correct POST method and request body = @PostMapping("/refresh") public ResponseEntity<TokenResponse> refreshToken(@RequestBody RefreshRequest request) [OK]

Hint: Refresh token requests use POST with @RequestBody [OK]

Common Mistakes:

• Using GET instead of POST
• Missing @RequestBody annotation
• Wrong return type or parameters

3.

Given the following Spring Boot service method, what will be the output if the refresh token is invalid?

public TokenResponse refreshAccessToken(String refreshToken) {
    if (!tokenRepository.existsByToken(refreshToken)) {
        throw new RuntimeException("Invalid refresh token");
    }
    // generate new access token
    return new TokenResponse("newAccessToken");
}

medium

A. Throws RuntimeException with message "Invalid refresh token"

B. Returns a new TokenResponse with "newAccessToken"

C. Returns null

D. Returns the old refresh token

Solution

1. Step 1: Analyze the token existence check

   The method checks if the refresh token exists in the repository; if not, it throws an exception.

2. Step 2: Determine behavior on invalid token

   Since the token is invalid, the method throws RuntimeException with the message "Invalid refresh token".

3. Final Answer:

   Throws RuntimeException with message "Invalid refresh token" -> Option A

4. Quick Check:

   Invalid token triggers exception = Throws RuntimeException with message "Invalid refresh token" [OK]

Hint: Invalid refresh token causes exception throw [OK]

Common Mistakes:

• Assuming method returns null on invalid token
• Thinking it returns old token instead
• Ignoring exception throwing

4.

Identify the error in this Spring Boot refresh token controller method:

@PostMapping("/refresh")
public ResponseEntity<TokenResponse> refreshToken(@RequestParam String refreshToken) {
    TokenResponse token = authService.refreshAccessToken(refreshToken);
    return ResponseEntity.ok(token);
}

What is the problem?

medium

A. Using @RequestParam instead of @RequestBody for refresh token

B. Missing @PostMapping annotation

C. Returning ResponseEntity instead of TokenResponse

D. Calling wrong service method

Solution

1. Step 1: Check parameter annotation

   The refresh token is usually sent in the request body as JSON, not as a query parameter.

2. Step 2: Identify correct annotation

   The method should use @RequestBody instead of @RequestParam to receive the refresh token properly.

3. Final Answer:

   Using @RequestParam instead of @RequestBody for refresh token -> Option A

4. Quick Check:

   Refresh token needs @RequestBody, not @RequestParam [OK]

Hint: Refresh token comes in body, use @RequestBody [OK]

Common Mistakes:

• Using query parameters for refresh token
• Confusing ResponseEntity with return type
• Missing or wrong annotations

5.

You want to implement a refresh token mechanism in Spring Boot that invalidates the old refresh token after use and issues a new one along with the access token. Which approach below correctly achieves this?

hard

A. Check refresh token validity, generate new access token, keep old refresh token unchanged

B. Generate new access token and new refresh token, save new refresh token, delete old refresh token

C. Generate new access token only, do not check refresh token validity

D. Delete refresh token without issuing new tokens

Solution

1. Step 1: Understand token rotation

   To improve security, the old refresh token should be invalidated and replaced with a new one after use.

2. Step 2: Identify correct token handling

   Generate new access token and new refresh token, save new refresh token, delete old refresh token correctly generates new access and refresh tokens, saves the new refresh token, and deletes the old one.

3. Final Answer:

   Generate new access token and new refresh token, save new refresh token, delete old refresh token -> Option B

4. Quick Check:

   Refresh token rotation = Generate new access token and new refresh token, save new refresh token, delete old refresh token [OK]

Hint: Rotate refresh tokens: new token saved, old token deleted [OK]

Common Mistakes:

• Not invalidating old refresh token
• Skipping refresh token validity check
• Deleting tokens without issuing new ones