14.22 From

   The From request-header field, if given, SHOULD contain an Internet
   e-mail address for the human user who controls the requesting user
   agent.  The address SHOULD be machine-usable, as defined by mailbox
   in RFC 822 (as updated by RFC 1123 ):

          From   = "From" ":" mailbox

   An example is:

          From: webmaster@w3.org

   This header field MAY be used for logging purposes and as a means for
   identifying the source of invalid or unwanted requests. It SHOULD NOT
   be used as an insecure form of access protection. The interpretation
   of this field is that the request is being performed on behalf of the
   person given, who accepts responsibility for the method performed. In
   particular, robot agents SHOULD include this header so that the
   person responsible for running the robot can be contacted if problems
   occur on the receiving end.





Fielding, et. al.           Standards Track                   [Page 118]

RFC 2068                        HTTP/1.1                    January 1997


   The Internet e-mail address in this field MAY be separate from the
   Internet host which issued the request. For example, when a request
   is passed through a proxy the original issuer's address SHOULD be
   used.

     Note: The client SHOULD not send the From header field without the
     user's approval, as it may conflict with the user's privacy
     interests or their site's security policy. It is strongly
     recommended that the user be able to disable, enable, and modify
     the value of this field at any time prior to a request.

14.23 Host

   The Host request-header field specifies the Internet host and port
   number of the resource being requested, as obtained from the original
   URL given by the user or referring resource (generally an HTTP URL,
   as described in section 3.2.2). The Host field value MUST represent
   the network location of the origin server or gateway given by the
   original URL. This allows the origin server or gateway to
   differentiate between internally-ambiguous URLs, such as the root "/"
   URL of a server for multiple host names on a single IP address.

          Host = "Host" ":" host [ ":" port ]    ; Section 3.2.2

   A "host" without any trailing port information implies the default
   port for the service requested (e.g., "80" for an HTTP URL). For
   example, a request on the origin server for
    MUST include:

          GET /pub/WWW/ HTTP/1.1
          Host: www.w3.org

   A client MUST include a Host header field in all HTTP/1.1 request
   messages on the Internet (i.e., on any message corresponding to a
   request for a URL which includes an Internet host address for the
   service being requested). If the Host field is not already present,
   an HTTP/1.1 proxy MUST add a Host field to the request message prior
   to forwarding it on the Internet. All Internet-based HTTP/1.1 servers
   MUST respond with a 400 status code to any HTTP/1.1 request message
   which lacks a Host header field.

   See sections 5.2 and 19.5.1 for other requirements relating to Host.