code: func NewV4SigningClientWithHTTPClient(creds *credentials.Credentials, region string, httpClient *http.Client) *http.Client {
  	return &http.Client{
  		Transport: Transport{
  			client: httpClient,
  			creds:  creds,
  			signer: v4.NewSigner(creds),
  			region: region,
  		},
  	}
  }
docs: // NewV4SigningClientWithHTTPClient returns an *http.Client that will sign all requests with AWS V4 Signing.