feat: add private auth foundation

backend/internal/auth/middleware.go

@@ -0,0 +1,28 @@
+package auth
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+const CurrentUserIDKey = "currentUserID"
+
+func RequireUser(tokenVerifier func(string) (uint, error)) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		header := c.GetHeader("Authorization")
+		token := strings.TrimPrefix(header, "Bearer ")
+		if token == "" || token == header {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "missing bearer token"})
+			return
+		}
+		userID, err := tokenVerifier(token)
+		if err != nil {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid bearer token"})
+			return
+		}
+		c.Set(CurrentUserIDKey, userID)
+		c.Next()
+	}
+}