code: func NewV4SigningClientWithHTTPClient(credentials awsauth.Credentials, httpClient *http.Client) *http.Client {
  	return &http.Client{
  		Transport: V4Transport{
  			HTTPClient:  httpClient,
  			Credentials: credentials,
  		},
  	}
  }
docs: // NewV4SigningClientWithHTTPClient returns an *http.Client that will sign all requests with AWS V4 Signing.