Proxy Web Servers and Authentication > How Proxies Work > Cache headers

Request

Headers used only in HTTP Requests.

Host

The Internet (DNS) host name and port number from the URL of the resource being requested.

Authorization

Used to send the user's credentials to the origin server. Typically a client will resend a request with an "Authorizations" header when it receives a "401 Unauthorized" status code and a "WWW-Authenticate" response header in response to a URL request.

Proxy-Authorization

Used to send the user's credentials to the chain of proxy servers servicing the request.

If-modified-since

Used in a request to make it conditional: if the requested resource has not been modified since the time specified in this field, the resource will not be returned from the server; instead, a 304 "Not modified" response will be returned without any message-body.

If-match

In combination with the "ETag" entity header, the server will return an 412 "Precondition failed" if the ETag of the entity being requested is different from the ETag of the entity on the server

If-none-match

The inverse of the "If-match" header operation. If the ETag of the entity being requested matches the ETag of the entity on the server, the server returns a 304 "Not Modified" status.