acl: Support PUT calls with success for 'private' ACL's (#9000)

Add dummy calls which respond success when ACL's
are set to be private and fails, if user tries
to change them from their default 'private'

Some applications such as nuxeo may have an
unnecessary requirement for this operation,
we support this anyways such that don't have
to fully implement the functionality just that
we can respond with success for default ACLs

cmd/api-errors.go

@@ -95,6 +95,7 @@ const (
 	ErrMissingContentLength
 	ErrMissingContentMD5
 	ErrMissingRequestBodyError
+	ErrMissingSecurityHeader
 	ErrNoSuchBucket
 	ErrNoSuchBucketPolicy
 	ErrNoSuchBucketLifecycle
@@ -471,6 +472,11 @@ var errorCodes = errorCodeMap{
 		Description:    "Missing required header for this request: Content-Md5.",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
+	ErrMissingSecurityHeader: {
+		Code:           "MissingSecurityHeader",
+		Description:    "Your request was missing a required header",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
 	ErrMissingRequestBodyError: {
 		Code:           "MissingRequestBodyError",
 		Description:    "Request body is empty.",
@@ -1803,6 +1809,13 @@ func toAPIError(ctx context.Context, err error) APIError {
 		// their internal error types. This code is only
 		// useful with gateway implementations.
 		switch e := err.(type) {
+		case *xml.SyntaxError:
+			apiErr = APIError{
+				Code: "MalformedXML",
+				Description: fmt.Sprintf("%s (%s)", errorCodes[ErrMalformedXML].Description,
+					e.Error()),
+				HTTPStatusCode: errorCodes[ErrMalformedXML].HTTPStatusCode,
+			}
 		case url.EscapeError:
 			apiErr = APIError{
 				Code: "XMinioInvalidObjectName",