Add auth middleware (#13506)

### What problem does this PR solve?

Use auth middle-ware to check authorization.

### Type of change

- [x] Refactoring

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/handler/common.go

@@ -0,0 +1,37 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package handler
+
+import (
+	"ragflow/internal/common"
+	"ragflow/internal/model"
+
+	"github.com/gin-gonic/gin"
+)
+
+func GetUser(c *gin.Context) (*model.User, common.ErrorCode, string) {
+	userAny, exist := c.Get("user")
+	if !exist {
+		return nil, common.CodeUnauthorized, "User not found"
+	}
+
+	user, ok := userAny.(*model.User)
+	if !ok {
+		return nil, common.CodeUnauthorized, "User not found"
+	}
+	return user, common.CodeSuccess, ""
+}