func (o *ObjectInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }

// KMSKeyID returns in AWS compatible KMS KeyID() format.
func (o *MultipartInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }

// kmsKeyIDFromMetadata returns any AWS S3 KMS key ID in the
// metadata, if any. It returns an empty ID if no key ID is
// present.
func kmsKeyIDFromMetadata(metadata map[string]string) string {

	case crypto.S3:
		m[xhttp.AmzServerSideEncryption] = xhttp.AmzEncryptionAES
	case crypto.S3KMS:
		m[xhttp.AmzServerSideEncryption] = xhttp.AmzEncryptionKMS
		m[xhttp.AmzServerSideEncryptionKmsID] = kmsKeyIDFromMetadata(metadata)
		if kmsCtx, ok := metadata[crypto.MetaContext]; ok {
			m[xhttp.AmzServerSideEncryptionKmsContext] = kmsCtx
		}
	case crypto.SSEC: