document content is to facilitate the scaling that caching permits.
   To support cookies, a caching proxy must obey these rules already in
   the HTTP specification:

   * Honor requests from the cache, if possible, based on cache validity
     rules.

   * Pass along a Cookie request header in any request that the proxy
     must make of another server.

   * Return the response to the client.  Include any Set-Cookie response
     header.






 
RFC 2109            HTTP State Management Mechanism        February 1997


   * Cache the received response subject to the control of the usual
     headers, such as Expires, Cache-control: no-cache, and Cache-
     control: private,

   * Cache the Set-Cookie subject to the control of the usual header,
     Cache-control: no-cache="set-cookie".  (The Set-Cookie header
     should usually not be cached.)

   Proxies must not introduce Set-Cookie (Cookie) headers of their own
   in proxy responses (requests).

5.  EXAMPLES

5.1  Example 1

   Most detail of request and response headers has been omitted.  Assume
   the user agent has no stored cookies.

     1.  User Agent -> Server

         POST /acme/login HTTP/1.1
         [form data]

         User identifies self via a form.

     2.  Server -> User Agent

         HTTP/1.1 200 OK
         Set-Cookie: Customer="WILE_E_COYOTE"; Version="1"; Path="/acme"

         Cookie reflects user's identity.

     3.  User Agent -> Server

         POST /acme/pickitem HTTP/1.1
         Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme"
         [form data]

         User selects an item for "shopping basket."

     4.  Server -> User Agent

         HTTP/1.1 200 OK
         Set-Cookie: Part_Number="Rocket_Launcher_0001"; Version="1";
                 Path="/acme"

         Shopping basket contains an item.





 
RFC 2109            HTTP State Management Mechanism        February 1997


     5.  User Agent -> Server

         POST /acme/shipping HTTP/1.1
         Cookie: $Version="1";
                 Customer="WILE_E_COYOTE"; $Path="/acme";
                 Part_Number="Rocket_Launcher_0001"; $Path="/acme"
         [form data]

         User selects shipping method from form.

     6.  Server -> User Agent

         HTTP/1.1 200 OK
         Set-Cookie: Shipping="FedEx"; Version="1"; Path="/acme"

         New cookie reflects shipping method.

     7.  User Agent -> Server

         POST /acme/process HTTP/1.1
         Cookie: $Version="1";
                 Customer="WILE_E_COYOTE"; $Path="/acme";