All you need to know about JSON Web Tokens(JWT) — Part 1/2

What is JWT?

How does JWT work?

The tokens are digitally signed by the server’s private key. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair (with RSA or ECDSA). Do note that with signed tokens, all the information contained within the token is exposed to users or other parties, even though they are unable to change it.

When to use JWT?

  1. To locally save user session at client side instead of the traditional approach of creating a session in the server and returning a cookie. This allows a stateless authentication mechanism as the user state is never saved in server memory.
  2. To reduce repeated database queries because JWTs are self-contained, that is, they have all the necessary information to allow an authenticated user to access all server resources and routes.
  3. To pass data in HTML and HTTP environments because of its small size. JSON is less verbose than XML so its encoded size is also smaller. It can be sent through a URL, POST parameter, or inside an HTTP header.
  4. To authenticate a user via single sign-on. This is the most common use case of JWT and can be easily used among systems of different domains.
  5. To exchange information as JWT is a good way to securely transmit information between parties because it can be signed by the sender. It also allows checking if the content has been tampered with.
  6. Additionally, JSON parsers are common in most programming languages, because they map directly to objects as compared to XML that doesn’t have a natural document-to-object mapping.
  1. Know the algorithms
  2. Use an appropriate key size

What JWT is not used for?

The data inside a JWT is encoded and signed, not encrypted. The purpose of encoding data is to transform the data structure. Signing data allows the data receiver to verify the source’s authenticity. So encoding and signing data does NOT secure the data. On the other hand, the main purpose of encryption is to secure data and prevent unauthorized access.

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  2. Check out Part 2 of this blog!



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Kanika Modi

Kanika Modi


Software Engineer 2 @amazon | Designing Systems At Scale | Invent & Simplify | Tech & Career Blogs | She/Her | ViewsMine()