20 JWT Token Interview Questions and Answers

JWT Token is a popular authentication method used by many web applications. When applying for a position that involves working with JWT Token, it is important to be prepared to answer questions about this authentication method. In this article, we review some of the most common JWT Token questions and provide guidance on how to answer them.

JWT Token Interview Questions and Answers

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

1. What is a JWT?

A JWT is a JSON Web Token, which is used to provide authentication and authorization for users accessing a web application. JWTs are typically used to store user information, such as name and email address, and are signed with a secret key to prevent tampering. When a user tries to access a protected resource, the JWT is sent to the server to be verified. If the JWT is valid, then the user is granted access to the resource.

2. Can you explain what JSON Web Token Authentication is?

JSON Web Token Authentication is a process of authenticating users using JSON Web Tokens. In this process, the user’s credentials are first verified and then a JSON Web Token is generated. This token is then sent to the user and is used by the user to authenticate with the server.

3. When should I use JWTs for authentication instead of sessions and cookies?

JWTs are best used when you need to store a lot of data on the client side that needs to be easily accessible, but that you don’t want to be tampered with. For example, if you are building an Single Page Application that needs to make API calls to a server, you might use a JWT to store information about the user’s session on the client side so that you can easily access it and make sure it hasn’t been tampered with.

4. Can you give me some examples of situations when it’s preferable to use JWT over other types of tokens like Auth0 or OAuth2?

JWT is preferable in situations where you want the client to be able to access resources on the server without having to go through an authorization server. This might be the case if the client and server are both owned by the same organization. JWT is also preferable if you want the client to be able to access resources on multiple servers, as it eliminates the need to get a new token from each server.

5. What are the advantages of using JSON Web Tokens (JWTs)?

JWTs offer a number of advantages over other forms of authentication, such as cookies or sessions. They are easy to use and implement, they are stateless, and they are more secure because they are signed and can be verified. JWTs can also be used to store additional information about the user, such as their permissions or roles.

6. How do you create a new token in python?

There are a few different ways to create a new token in python. One way is to use the jwt library, which you can install using pip. Once you have the library installed, you can use the jwt.encode() function to create a new token.

7. How do you verify an existing token in python?

There are a few ways to do this, but the most common is to use the PyJWT library. With this library, you can simply call the jwt.decode() function and pass in the token as a string. This will return the decoded payload, which you can then use to verify the contents of the token.

8. What is the difference between signed and encrypted tokens?

A signed token is one that has been signed by the issuer using a secret key. This signature can be verified by anyone who has the secret key. An encrypted token is one that has been encrypted by the issuer using a secret key. This token can only be decrypted by someone who has the secret key.

9. Why would you prefer one over the other?

There is no one-size-fits-all answer to this question, as the best option for you will depend on your specific needs and preferences. However, some reasons you might prefer JWT over other options include its compact size (which makes it ideal for sending over the internet), its support for multiple signature algorithms, and its built-in expiration mechanism.

10. Are there any limitations on the size of data that can be stored in a JWT?

There are no size limitations on the data that can be stored in a JWT, but keep in mind that the larger the data, the larger the token will be. This can impact performance, so it is something to keep in mind when deciding what data to include in a JWT.

11. If so, how would you work around this issue?

There are a few ways to work around this issue:

– Use a different type of token that doesn’t have this issue, such as an opaque token.
– Use a JWT with a short expiration time, and make sure to refresh it often.
– Use a JWT with a long expiration time, but make sure to check the token’s validity on each request.

12. Is there any way to revoke a token once it has been issued?

There is no built-in way to revoke a token once it has been issued, but there are some workarounds that can be used. One approach is to keep track of all the tokens that have been issued and then invalidate any token that is on that list. Another approach is to have a short expiration time for the tokens, so that they will automatically expire and become invalid.

13. Does a JWT have expiry time?

No, a JWT does not have an expiry time.

14. If yes, then how does it get generated?

JWT tokens are generated using a secret key and a hashing algorithm. The secret key is used to sign the token, and the hashing algorithm is used to encrypt the token. The resulting token is a string of characters that can be used to verify the identity of the user.

15. What happens if you try to access an expired token?

If you try to access an expired token, you will receive an error message.

16. What type of algorithm is used to sign a JWT?

The algorithm used to sign a JWT is known as the JSON Web Signature algorithm, or JWS. This algorithm is used to create a digital signature that can be used to verify the authenticity of a JWT.

17. Which algorithms should we avoid using with JWT?

There are a few algorithms which should be avoided when using JWT, as they are either no longer considered secure or have known vulnerabilities. These include the HS* algorithms, as well as the RS* and ES* algorithms prior to their respective SHA-2 versions.

18. What are the common methods of storing JWT in your application?

There are a few different ways that you can store your JWT in your application. The most common methods are either to store it in a cookie or to store it in local storage.

19. Is it possible to encrypt a JWT without signing it?

No, it is not possible to encrypt a JWT without signing it. The JWT specification requires that a JWT be signed in order to be considered valid.

20. What are some good practices for creating secure auth APIs using JWT?

Some good practices for creating secure auth APIs using JWT include using HTTPS for all communications, verifying the JWT signature, and only accepting JWTs from trusted sources.