code: func (b *BackendConfig) addHeadersAndHost(req *http.Request) *http.Request {
  	if b.Options.Hostname != "" {
  		req.Host = b.Options.Hostname
  	}
  
  	for k, v := range b.Options.Headers {
  		req.Header.Set(k, v)
  	}
  	return req
  }
docs: // this function adds additional http headers and hostname to http.request