305 Use Proxy

   The requested resource MUST be accessed through the proxy given by
   the Location field. The Location field gives the URI of the proxy.
   The recipient is expected to repeat this single request via the
   proxy. 305 responses MUST only be generated by origin servers.

      Note: RFC 2068 was not clear that 305 was intended to redirect a
      single request, and to be generated by origin servers only.  Not
      observing these limitations has significant security consequences.