Someone

<IfModule mod_proxy.c>

        #turning ProxyRequests on and allowing proxying from all may allow
        #spammers to use your proxy to send email.

        ProxyRequests Off

        <Proxy *>
                Order deny,allow
                Deny from all
                #Allow from .your_domain.com
        </Proxy>

        # Enable/disable the handling of HTTP/1.1 "Via:" headers.
        # ("Full" adds the server version; "Block" removes all outgoing Via: headers)
        # Set to one of: Off | On | Full | Block

        ProxyVia On

        # To enable the cache as well, edit and uncomment the following lines:
        # (no cacheing without CacheRoot)

        CacheRoot "/var/cache/apache2/proxy"
        CacheSize 5
        CacheGcInterval 4
        CacheMaxExpire 24
        CacheLastModifiedFactor 0.1
        CacheDefaultExpire 1
        # Again, you probably should change this.
        #NoCache a_domain.com another_domain.edu joes.garage_sale.com

</IfModule>