: The request started from a related subdomain. The "Post" Connection
This looks like you're piecing together the technical components of , specifically those used for Cross-Origin Resource Sharing (CORS) and Cross-Site Request Forgery (CSRF) protection. The Concept: Fetch Metadata ( sec-fetch-* )
— Indicates the "what" (data fetch, not an image or script). sec,fetch,site:,cross,site
— Indicates the "where" (different domain).
When you send a request (like submitting a login form or updating account settings), the browser automatically attaches these headers. A secure server will check them to prevent attacks: : The request started from a related subdomain
: This is the most critical header in your list. It tells the server the relationship between the request initiator's origin and the target resource's origin.
: The server sees cross-site on a sensitive POST action and rejects it because it knows this request didn't originate from its own trusted frontend. Summary of the Headers — Indicates the "where" (different domain)
: The browser adds sec-fetch-site: cross-site and sec-fetch-mode: navigate (or cors ).