HTTP Cookies

Client-side data packets: they enable state management (like user authentication) over the inherently stateless HTTP protocol.

HTTP Cookies are small, client-side key-value data stores, typically limited to 4 KB per cookie, that allow a server to maintain state across multiple requests. The server initiates a cookie using the `Set-Cookie` response header, instructing the client browser to store it. The browser then automatically includes that cookie in the `Cookie` request header for all relevant future requests to the same domain. Primary applications are session management (a `sessionID` for login status), user personalization, and tracking. For security, developers must utilize attributes like `HttpOnly` (to block JavaScript access, mitigating XSS) and `Secure` (to enforce transmission over HTTPS) to protect sensitive data.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies