Refresh token pattern in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a refresh token field in a Spring Boot entity.

Spring Boot

private String [1];

Drag options to blanks, or click blank then click option'

AtokenExpiry

BaccessToken

CuserId

DrefreshToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'accessToken' instead of 'refreshToken'.

Naming the field unrelated to tokens.

The field refreshToken stores the refresh token string in the entity.

2fill in blank

medium

Complete the code to generate a new refresh token string using UUID.

Spring Boot

String newRefreshToken = UUID.[1]().toString();

Drag options to blanks, or click blank then click option'

ArandomUUID

BnewUUID

CgenerateUUID

DcreateUUID

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like 'newUUID()'.

Confusing with other UUID methods.

The method randomUUID() generates a unique UUID string for refresh tokens.

3fill in blank

hard

Fix the error in the method signature for refreshing tokens in a Spring Boot controller.

Spring Boot

public ResponseEntity<?> [1](@RequestBody TokenRefreshRequest request) {

Drag options to blanks, or click blank then click option'

ArefreshAccessToken

BrefreshToken

CgetToken

DupdateToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using vague method names like 'getToken'.

Using names that do not indicate refreshing.

The method name refreshAccessToken clearly indicates its purpose to refresh the access token using the refresh token.

4fill in blank

hard

Fill both blanks to complete the code that validates the refresh token and generates a new access token.

Spring Boot

if (tokenService.validate[1](request.get[2]())) {
    String accessToken = tokenService.createAccessToken();
}

Drag options to blanks, or click blank then click option'

ARefreshToken

BAccessToken

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing access token and refresh token in validation.

Using incorrect method names.

The method validateRefreshToken checks the refresh token validity, and getRefreshToken() retrieves it from the request.

5fill in blank

hard

Fill all three blanks to complete the code that creates a response with the new access token, refresh token, and token type.

Spring Boot

return ResponseEntity.ok(new TokenRefreshResponse([1], [2], [3]));

Drag options to blanks, or click blank then click option'

AaccessToken

B"Bearer"

CrefreshToken

D"Token"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping access token and refresh token positions.

Using incorrect token type strings.

The response includes the new accessToken, the token type "Bearer", and the refreshToken.

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