How do CORS and CSP affect each other?

CORS (Cross-Origin Resource Sharing) and CSP (Content Security Policy) are two different security mechanisms that affect how the browser interacts with resources, but they operate at different levels.

• CORS controls which external domains can make requests to your server (e.g., AJAX requests). It is a server policy that informs the browser whether requests from another origin are allowed.

• CSP is a security policy that restricts where the browser can load resources from (scripts, styles, images, etc.) and execute them. CSP helps prevent XSS attacks.

Interaction:

• If CORS disallows a request, the browser will not perform the request to the server from another domain.
• If CSP disallows loading or executing a resource, even if CORS permits the request, the resource will not be used.

Example: if your site loads a script from another domain, that domain's server must allow CORS requests, and your CSP must permit loading scripts from that domain.

Thus, CORS and CSP complement each other, providing comprehensive protection when working with external resources.