code: public static Headers varyHeaders(Response response) {
      // Use the request headers sent over the network, since that's what the
      // response varies on. Otherwise OkHttp-supplied headers like
      // "Accept-Encoding: gzip" may be lost.
      Headers requestHeaders = response.networkResponse().request().headers();
      Headers responseHeaders = response.headers();
      return varyHeaders(requestHeaders, responseHeaders);
    }
docs: Returns the subset of the headers in {@code response}'s request that impact the content of
  response's body.