I-D ACTION:draft-mogul-http-revalidate-00.txt

Excerpted, from the IETF mailing list:

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 A New Internet-Draft is available from the on-line Internet-Drafts 
 directories.                                                              

       Title     : Forcing HTTP/1.1 proxies to revalidate responses        
       Author(s) : J. Mogul
       Filename  : draft-mogul-http-revalidate-00.txt
       Pages     : 10
       Date      : 01/07/1997

The HTTP/1.1 specification [1] currently defines a ``proxy-revalidate'' 
Cache-control directive, which forces a proxy to revalidate a stale 
response before using it in a reply.  There is no mechanism defined that 
forces a proxy, but not an end-client, to revalidate a fresh response.  The
lack of such a mechanism is due to an error in drafting RFC2068, and 
appears to create problems for use of the Authorization header, the Digest 
Access Authentication extension [2], the State Management Mechanism [3], 
and several other proposed extensions.  This document discusses the problem
and several possible solutions, and proposes to add a new ``proxy-maxage'' 
directive as the best available solution.                                  

ftp://ds.internic.net/internet-drafts/draft-mogul-http-revalidate-00.txt

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-Jeff