20 JWT Authentication Interview Questions and Answers

JWT Authentication is a process of verifying the identity of a user by using a JSON Web Token. This token is then used to access protected resources. JWT Authentication is a popular authentication method for web applications and APIs. If you are interviewing for a position that involves JWT Authentication, it is important to be prepared to answer questions about this process. In this article, we discuss the most commonly asked JWT Authentication questions and how you should respond.

JWT Authentication Interview Questions and Answers

Here are 20 commonly asked JWT Authentication interview questions and answers to prepare you for your interview:

1. What is a JWT or JSON Web Token?

A JWT is a JSON Web Token, which is an open standard that defines a way to securely transmit information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be used to authenticate users or to exchange information between parties, and are often used in Single Sign-On (SSO) scenarios.

2. Can you explain the structure of a JSON Web Token and what each part means?

A JSON Web Token (JWT) is made up of three parts: the header, the payload, and the signature. The header contains information about the token, such as the type of token and the algorithm used to generate the signature. The payload is the actual data that is being encoded, such as the user’s ID or email address. The signature is used to verify that the token has not been tampered with.

3. Is it possible to encrypt the contents of a JSON Web Token? If yes, how would you do that?

Yes, it is possible to encrypt the contents of a JSON Web Token. This can be done by using a library that supports the JSON Web Token standard, such as the jose-jwt library.

4. How secure are JSON Web Tokens? What security issues should one be aware of when using them?

JSON Web Tokens are a very secure way to authenticate users. The main security issue to be aware of is that they should never be stored in plain text. If a JWT is stolen, then the attacker will have access to the user’s data.

5. Why are signed tokens used in authentication?

Signed tokens are used in authentication to ensure that the token has not been tampered with. If a token is tampered with, then it will no longer be valid and the user will not be able to authenticate. This helps to ensure the security of the authentication process.

6. What do you understand about the symmetric-key signature algorithm for JWT?

The symmetric-key signature algorithm is a way to ensure that a JWT has not been tampered with. Basically, it uses a shared secret between the issuer and the receiver of the JWT. The shared secret is used to generate a signature for the JWT, which is then checked by the receiver to make sure that it matches the signature that they have. If the signatures do not match, then the JWT is considered to be invalid.

7. What do you understand about the public-key signature algorithm for JWT?

The public-key signature algorithm for JWT is a way to ensure that a JSON Web Token has not been tampered with. In order to do this, a digital signature is created using a private key. This signature can then be verified using the public key, which is included in the JWT header. If the signature does not match, then it is likely that the JWT has been tampered with and should not be trusted.

8. What is an example use case where you would use the asymmetric encryption scheme for JWT signature?

One example use case where you would use the asymmetric encryption scheme for JWT signature is when you are working with a microservices architecture. In this type of architecture, it is common for there to be a central authentication service that is responsible for generating and validating JWTs. In order to ensure that only the authentication service can generate valid JWTs, you would use an asymmetric encryption scheme for the JWT signature. This would ensure that only the authentication service has the private key needed to generate a valid signature, and thus only the authentication service can generate valid JWTs.

9. Is it safe to pass JWTs over insecure channels like plain HTTP?

No, it is not safe to pass JWTs over insecure channels like plain HTTP. JWTs should only be passed over secure channels like HTTPS.

10. Is it safe to transmit JWTs without any additional layer of encryption on top of HTTPS?

While JWTs are often used in conjunction with HTTPS to provide an additional layer of security, it is technically possible to transmit JWTs without HTTPS. However, this is generally not considered to be a best practice, as it opens up the possibility of someone intercepting the JWT and being able to read its contents. For this reason, it is generally recommended that JWTs always be transmitted over HTTPS to help ensure their security.

11. Can you give me some examples of real world applications that use JWT?

JWT is used by many different applications, but some examples include:

– Single sign-on (SSO)
– Identity management
– API authentication

12. What’s the difference between sessions and JWT? Which one would you prefer in certain situations?

The main difference between sessions and JWT is that sessions are stored on the server, while JWT are stored on the client. JWT are generally preferred because they are more secure and can be used across multiple servers.

13. What are the main benefits of using JWT instead of other forms of authentication like sessions?

JWT is a stateless form of authentication, which means that there is no need to store any information about the user on the server. This can be a big advantage in terms of scalability, as it means that the server does not need to keep track of a large number of active sessions. JWT is also generally considered to be more secure than other forms of authentication, as it is more difficult to tamper with the token once it has been generated.

14. When should you use stateless authentication with JWT?

Stateless authentication is a good choice when you want to scale your authentication system horizontally. Because JWT tokens can be verified without having to query a database, they can be verified quickly and easily. This makes stateless authentication with JWT a good choice for high-traffic applications.

15. What are the most common problems associated with session management?

The most common problems associated with session management are session hijacking and session fixation. Session hijacking occurs when an attacker is able to take over a user’s session by stealing their session ID. Session fixation occurs when an attacker is able to control what session ID a user is given, which can allow the attacker to hijack the session or impersonate the user.

16. What is the best way to store JWTs?

The best way to store JWTs is by using a secure and reliable storage mechanism, such as a database. This will ensure that the JWTs are not lost or stolen, and that they can be easily retrieved when needed.

17. Is it possible to revoke access of already issued tokens if they’re compromised?

Yes, it is possible to revoke access of already issued tokens if they’re compromised. You can do this by invalidating the token or by blacklistsing the token.

18. What happens if a token expires?

If a token expires, then the user will no longer be able to access the protected resources that they were previously able to access. In order to regain access, they will need to generate a new token.

19. Can you give me some examples of real world companies that offer APIs that use JWT?

Some companies that use JWT for their APIs include Google, Microsoft, and Amazon.

20. How can you validate a JWT?

There are a few different ways to validate a JWT. One way is to use a library that can decode and verify the JWT for you. Another way is to manually decode the JWT and then verify the signature yourself.