JWT structure (header, payload, signature) in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create the JWT header with the correct algorithm.

Spring Boot

Map<String, Object> header = new HashMap<>();
header.put("alg", "[1]");

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

ASHA256

BRSA

CHS256

DMD5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'SHA256' directly instead of 'HS256'.

Using 'MD5' which is insecure and not standard for JWT.

The JWT header must specify the algorithm used for signing. "HS256" is the common HMAC SHA-256 algorithm used in JWT.

2fill in blank

medium

Complete the code to add the subject claim to the JWT payload.

Spring Boot

Map<String, Object> payload = new HashMap<>();
payload.put("sub", "[1]");

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Ausername

Bsubject

CuserId

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the literal word 'subject' instead of the username.

Using 'token' which is unrelated to the 'sub' claim.

The "sub" claim in JWT payload usually holds the username or user identifier string.

3fill in blank

hard

Fix the error in signing the JWT token with the secret key.

Spring Boot

String token = Jwts.builder()
  .setHeader(header)
  .setClaims(payload)
  .signWith(Keys.hmacShaKeyFor("[1]".getBytes()))
  .compact();

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Amysecret

Bkey

Csecret

Dmysecretkeymysecretkeymysecretkeymysecretkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using too short secret keys causing runtime errors.

Using generic words like 'key' or 'secret' without enough length.

The secret key for HS256 must be long enough (at least 256 bits). A short key like 'mysecret' is invalid and causes errors.

4fill in blank

hard

Fill both blanks to decode the JWT token and extract the payload claims.

Spring Boot

Claims claims = Jwts.parserBuilder()
  .setSigningKey(Keys.hmacShaKeyFor("[1]".getBytes()))
  .build()
  .[2](token)
  .getBody();

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Amysecretkeymysecretkeymysecretkeymysecretkey

BparseClaimsJws

CparsePlaintextJwt

Dmysecret

Attempts:

3 left

💡 Hint

Common Mistakes

Using a short secret key that doesn't match the signing key.

Using parsePlaintextJwt which is for unsigned tokens.

To parse a signed JWT, use the long secret key and the method parseClaimsJws(token) to get the claims body.

5fill in blank

hard

Fill all three blanks to build a JWT token with header, payload, and signature.

Spring Boot

String jwt = Jwts.builder()
  .setHeaderParam("typ", "[1]")
  .setSubject("[2]")
  .signWith(Keys.hmacShaKeyFor("[3]".getBytes()))
  .compact();

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

AJWT

Buser123

Cmysecretkeymysecretkeymysecretkeymysecretkey

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'token' instead of 'JWT' for header type.

Using short or invalid secret keys.

Putting literal words instead of actual username.

The header type is "JWT", the subject is the username like "user123", and the secret key must be long enough for signing.