Authentication with JWT token in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to generate a JWT token using the secret key.

Spring Boot

String token = Jwts.builder().setSubject(username).signWith([1]).compact();

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AKeys.hmacShaKeyFor(secret.getBytes())

Bnew SecretKeySpec(secret.getBytes(), "HmacSHA256")

CMac.getInstance("HmacSHA256")

DSecretKeyFactory.getInstance("PBKDF2WithHmacSHA256")

Attempts:

3 left

💡 Hint

Common Mistakes

Using Mac or SecretKeyFactory directly instead of Keys utility.

Passing raw secret string instead of a Key object.

The signWith method requires a Key object. Using Keys.hmacShaKeyFor(secret.getBytes()) correctly creates the key for signing the JWT.

2fill in blank

medium

Complete the code to extract the username from the JWT token.

Spring Boot

String username = Jwts.parserBuilder().setSigningKey([1]).build().parseClaimsJws(token).getBody().getSubject();

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AKeys.hmacShaKeyFor(secret.getBytes())

Bsecret

Ctoken

Dnew SecretKeySpec(secret.getBytes(), "HmacSHA256")

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the raw secret string instead of a Key object.

Passing the token string as the key.

The parser needs the signing key as a Key object to verify the token signature. Using Keys.hmacShaKeyFor(secret.getBytes()) provides the correct key.

3fill in blank

hard

Fix the error in the code that validates the JWT token expiration.

Spring Boot

boolean isValid = !Jwts.parserBuilder().setSigningKey(key).build().parseClaimsJws(token).getBody().getExpiration().[1](new Date());

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AcompareTo

Bafter

Cequals

Dbefore

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'after' without negation causes wrong validation.

Using 'equals' or 'compareTo' incorrectly.

The token is valid if its expiration date is after the current date. Using before checks if expiration is before now, so negating it means valid if expiration is in the future.

4fill in blank

hard

Fill both blanks to create a JWT token with expiration time set to 1 hour from now.

Spring Boot

String token = Jwts.builder().setSubject(user).setExpiration(new Date(System.currentTimeMillis() [1] [2])).signWith(key).compact();

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A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition.

Using division or wrong operators.

To set expiration 1 hour from now, add 1 hour in milliseconds to current time. 1 hour = 60 * 60 * 1000 ms, so use System.currentTimeMillis() + 60 * 60 * 1000.

5fill in blank

hard

Fill all three blanks to parse the JWT token, extract claims, and get the 'roles' claim as a list.

Spring Boot

Claims claims = Jwts.parserBuilder().setSigningKey([1]).build().parseClaimsJws(token).getBody(); List<String> roles = claims.get([2], [3]);

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Akey

B"roles"

CList.class

DString.class

Attempts:

3 left

💡 Hint

Common Mistakes

Using String.class instead of List.class for roles.

Passing raw secret string instead of key.

The signing key is needed to parse the token. The 'roles' claim is extracted by its name as a List, so use claims.get("roles", List.class).