code: func ResolveAuthPerHost(authPerHost map[string]Headerer) map[string]http.Header {
  	hostHeaders := make(map[string]http.Header, len(authPerHost))
  	for k, v := range authPerHost {
  		hostHeaders[k] = v.GetHeader()
  	}
  	return hostHeaders
  }
docs: // ResolveAuthPerHost takes a map of strings to Headerer and resolves the
  // Headerers to http.Headers