JWT structure (header, payload, signature) in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does the JWT header typically contain?

In a JWT token, the header part is a JSON object. What information does it usually hold?

A The user's personal data like name and email

B The signature to verify the token's authenticity

C The expiration date and issued time of the token

D The algorithm used for signing and the token type

💡 Hint

Think about what the system needs to know to verify the token's signature.

The JWT header contains metadata about the token, mainly the signing algorithm (e.g., HS256) and the token type (usually 'JWT').

❓ component_behavior

intermediate

What is stored in the JWT payload?

The payload section of a JWT contains claims. What kind of information is typically stored here?

A The algorithm used for signing the token

B The secret key used to sign the token

C Claims about the user and token metadata like expiration

D The encoded signature of the token

💡 Hint

Think about what data the server wants to share securely with the client.

The payload contains claims such as user ID, roles, and token expiration time.

📝 Syntax

advanced

What is the correct order of JWT parts?

A JWT token is made of three parts separated by dots. What is the correct order of these parts?

A Signature, Header, Payload

B Header, Payload, Signature

C Payload, Header, Signature

D Payload, Signature, Header

💡 Hint

Remember the token looks like three base64 strings separated by dots.

The JWT format is: base64UrlEncode(header).base64UrlEncode(payload).base64UrlEncode(signature).

🔧 Debug

advanced

Why does this JWT signature verification fail?

Given a JWT token, the signature verification fails in Spring Boot. Which of these is the most likely cause?

A The secret key used to sign the token is different from the one used to verify it

B The payload contains user data instead of metadata

C The header is missing the 'typ' field

D The token has three parts separated by dots

💡 Hint

Think about what must match exactly to verify a signature.

Signature verification requires the same secret key used for signing. If keys differ, verification fails.

🧠 Conceptual

expert

What is the role of the JWT signature?

Why is the signature part important in a JWT token?

A It ensures the token has not been altered and confirms the sender's identity

B It stores the user's password securely

C It contains the expiration date of the token

D It holds the user's profile information

💡 Hint

Think about how the server trusts the token's data.

The signature is created by signing the header and payload with a secret key. It helps verify the token's integrity and authenticity.