Why JWT Is Replacing Cookies for Stateless Web Authentication

1. HTTP's Statelessness

HTTP is a stateless protocol; it does not retain any information about previous requests or responses. Consequently, a web page that requires login cannot remember that a user is already authenticated unless additional data is sent with each request.

The stateless nature reduces CPU and memory usage on the server and makes the protocol simple and widely applicable.

2. Introduction of Cookie Technology

To avoid burdening the server with full client‑side state, the Cookie mechanism was introduced. The server sends a Set‑Cookie header; the client stores the cookie and automatically includes it in subsequent requests.

Images illustrate requests without cookies, with cookies, and the detailed cookie transmission process.

3. Form‑Based Authentication

Most user authentication today relies on form‑based login, which uses cookies to manage a session. After a successful login, the server creates a session object, stores the session ID in a cookie, and validates the session ID on each subsequent request.

When the client presents the cookie containing the session ID, the server checks the corresponding session object; if it exists, authentication succeeds.

4. Session Storage and Cluster Issues

Sessions are stored in the web server (e.g., Tomcat) and identified by a SessionID, usually via a cookie. In a clustered environment with load balancers like Nginx, a user may be directed to a different server that lacks the session data, causing login failures.

One solution is to centralize session storage using an external store such as Redis, which Spring Session can integrate with to achieve unified session management across the cluster.

5. Session vs. Cookie – Pain Points

Both aim to overcome HTTP's statelessness, but cookies store all data client‑side, exposing it to security risks (e.g., XSS, cross‑domain cookie theft). Sessions keep most data server‑side, but require reliable shared storage and add complexity.

These drawbacks motivate the search for a lighter solution: JWT.

6. What Is JWT?

JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting claims between parties. It is compact, URL‑safe, and can be signed or encrypted.

Key characteristics:

Small size allows transmission via URL, POST parameters, or HTTP headers.

The payload contains all necessary user information, reducing database lookups.

Typical use cases:

Authentication – after login, the server returns a JWT; the client includes it in the Authorization: Bearer <token> header for protected resources.

Information exchange – JWTs can be signed to verify the sender and ensure integrity.

7. JWT Structure

A JWT consists of three Base64‑URL‑encoded parts separated by dots:

Header – specifies token type and signing algorithm.

Payload – contains claims (registered, public, or private).

Signature – created by signing the header and payload with a secret or private key. xxxxx.yyyyy.zzzzz The header is a JSON object (e.g., {"alg":"HS256","typ":"JWT"}) that is Base64‑encoded. The payload includes claims such as iss, sub, aud, exp, nbf, iat, and jti. The signature verifies the token’s authenticity and integrity.

iss: token issuer sub: subject aud: audience exp: expiration time nbf: not before iat: issued at jti: unique identifier

8. How JWT Works

Upon successful login, the server returns a JWT. The client stores it (typically in local storage) and sends it in the Authorization header for subsequent requests. The server validates the token’s signature and claims; if valid, access is granted.

This stateless approach eliminates server‑side session storage, reduces database queries, and simplifies scaling.

9. Summary of Advantages and Security Considerations

Advantages:

Language‑agnostic – supported by Java, JavaScript, Node.js, PHP, etc.

Payload can carry non‑sensitive business data.

Compact size makes transmission efficient.

No server‑side session storage needed, facilitating horizontal scaling.

Security notes:

Never store sensitive data in the payload, as it is readable by the client.

Protect the secret/private key used for signing.

Always use HTTPS to prevent token interception.

10. Outlook

Future articles will cover JWT usage patterns, pros and cons, and techniques to secure tokens.