CSRFTokens

CSRFTokens are a security mechanism used to prevent Cross-Site Request Forgery. They rely on unpredictable tokens issued by the server and associated with a user session or a particular form. When the client submits a request that could change state on the server (such as form submission or an API call), the request must include a valid token. The server validates the token and rejects requests that lack a token or present an incorrect value.

Tokens are typically generated as cryptographically random strings and are stored in a server-side session or in a per-form data store. They are delivered to the client either as a hidden form field, as a custom HTTP header in AJAX requests, or via a synchronizer mechanism, and then returned with the state-changing request. Tokens can be per-session, per-form, or rotated after use to limit reuse.

There are several common patterns for implementing CSRFTokens. In the synchronizer token pattern, the server stores the token and requires it with each request. In the double-submit cookie pattern, the token is placed in a cookie and also in a request header or form field; the server compares both values. Many frameworks provide built-in CSRF protection and authentication integration.

Security considerations include using secure, unpredictable tokens, transmitting them over HTTPS, and avoiding token leakage through browser history, logs, or XSS. Additional defenses include same-site cookies and strict validation of state-changing operations. While CSRFTokens help mitigate CSRF risks, they do not protect against all attacks and should be combined with other security controls.