add auth module

backend/internal/auth/middleware.go

@@ -0,0 +1,36 @@
+package auth
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+func AuthMiddleware(secret []byte) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		authHeader := c.GetHeader("Authorization")
+		if authHeader == "" {
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "missing authorization header"})
+			c.Abort()
+			return
+		}
+
+		tokenString := strings.TrimPrefix(authHeader, "Bearer ")
+		if tokenString == authHeader {
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid authorization header"})
+			c.Abort()
+			return
+		}
+
+		claims, err := ParseToken(tokenString, secret)
+		if err != nil {
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid token"})
+			c.Abort()
+			return
+		}
+
+		c.Set("userID", claims.UserID)
+		c.Next()
+	}
+}