Labels on a web exchange
When your browser asks for a page, its request may identify the browser (User-Agent) or carry a cookie from a sign-in. The website’s reply may include Content-Type to say what kind of content it sent and Cache-Control to say whether and how long a saved copy may be used.
These headers travel alongside the page or other data. They help the browser and server decide how to handle the exchange.
Some headers need care
An Authorization header may contain an access token. Logging or sharing that header, or a sign-in cookie, could let someone else use the account. An incorrect header can also cause a browser to mishandle an otherwise valid reply.