consistent error message if auth is not setup

fix https://github.com/seaweedfs/seaweedfs/issues/6262

weed/s3api/s3api_object_handlers_multipart.go

@@ -228,8 +228,8 @@ func (s3a *S3ApiServer) PutObjectPartHandler(w http.ResponseWriter, r *http.Requ
 	}
 
 	dataReader := r.Body
+	rAuthType := getRequestAuthType(r)
 	if s3a.iam.isEnabled() {
-		rAuthType := getRequestAuthType(r)
 		var s3ErrCode s3err.ErrorCode
 		switch rAuthType {
 		case authTypeStreamingSigned:
@@ -243,6 +243,11 @@ func (s3a *S3ApiServer) PutObjectPartHandler(w http.ResponseWriter, r *http.Requ
 			s3err.WriteErrorResponse(w, r, s3ErrCode)
 			return
 		}
+	} else {
+		if authTypeStreamingSigned == rAuthType {
+			s3err.WriteErrorResponse(w, r, s3err.ErrAuthNotSetup)
+			return
+		}
 	}
 	defer dataReader.Close()