On Thu 28 Feb 2008, J. Peng wrote:
> Also I checked apache's official document for mod_rewrite:
> http://httpd.apache.org/docs/2.0/mod/mod_rewrite.html

Well, Apache 2.2 can, see

Other things you should be aware of:
4. %{HTTP:header}, where header can be any HTTP MIME-header name, can always
be used to obtain the value of a header sent in the HTTP request.
Example: %{HTTP:Proxy-Connection} is the value of the HTTP header

I wasn't aware that this is a feature only of 2.2+.