code: public void sign(SignableRequest<?> request, AWSCredentials credentials)
              throws SdkClientException {
          sign(request, SignatureVersion.V2, SigningAlgorithm.HmacSHA256, credentials);
      }
docs: This signer will add "Signature" parameter to the request. Default
  signature version is "2" and default signing algorithm is "HmacSHA256".
  
  AWSAccessKeyId SignatureVersion SignatureMethod Timestamp Signature
  
  @param request
  request to be signed.
  @param credentials
  The credentials used to use to sign the request.