filter_response (HTTPClient::ProxyAuth)

    # File lib/httpclient/auth.rb, line 184
        def filter_response(req, res)
          command = nil
          if res.status == HTTP::Status::PROXY_AUTHENTICATE_REQUIRED
            if challenge = parse_authentication_header(res, 'proxy-authenticate')
              uri = req.header.request_uri
              challenge.each do |scheme, param_str|
                @authenticator.each do |auth|
                  if scheme.downcase == auth.scheme.downcase
                    challengeable = auth.challenge(uri, param_str)
                    command = :retry if challengeable
                  end
                end
              end
              # ignore unknown authentication scheme
            end
          end
          command
        end