feat: add Cache-Control: private, no-store to all API routes per default (#1126)

backend/internal/bootstrap/router_bootstrap.go

@@ -63,6 +63,7 @@ func initRouterInternal(db *gorm.DB, svc *services) (utils.Service, error) {
 	rateLimitMiddleware := middleware.NewRateLimitMiddleware().Add(rate.Every(time.Second), 60)
 
 	// Setup global middleware
+	r.Use(middleware.NewCacheControlMiddleware().Add())
 	r.Use(middleware.NewCorsMiddleware().Add())
 	r.Use(middleware.NewCspMiddleware().Add())
 	r.Use(middleware.NewErrorHandlerMiddleware().Add())

backend/internal/middleware/cache_control.go

@@ -0,0 +1,26 @@
+package middleware
+
+import "github.com/gin-gonic/gin"
+
+// CacheControlMiddleware sets a safe default Cache-Control header on responses
+// that do not already specify one. This prevents proxies from caching
+// authenticated responses that might contain private data.
+type CacheControlMiddleware struct {
+	headerValue string
+}
+
+func NewCacheControlMiddleware() *CacheControlMiddleware {
+	return &CacheControlMiddleware{
+		headerValue: "private, no-store",
+	}
+}
+
+func (m *CacheControlMiddleware) Add() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if c.Writer.Header().Get("Cache-Control") == "" {
+			c.Header("Cache-Control", m.headerValue)
+		}
+
+		c.Next()
+	}
+}

backend/internal/middleware/cache_control_test.go

@@ -0,0 +1,45 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCacheControlMiddlewareSetsDefault(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	router.Use(NewCacheControlMiddleware().Add())
+
+	router.GET("/test", func(c *gin.Context) {
+		c.Status(http.StatusOK)
+	})
+
+	req := httptest.NewRequest(http.MethodGet, "/test", http.NoBody)
+	w := httptest.NewRecorder()
+
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, "private, no-store", w.Header().Get("Cache-Control"))
+}
+
+func TestCacheControlMiddlewarePreservesExistingHeader(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	router.Use(NewCacheControlMiddleware().Add())
+
+	router.GET("/custom", func(c *gin.Context) {
+		c.Header("Cache-Control", "public, max-age=60")
+		c.Status(http.StatusOK)
+	})
+
+	req := httptest.NewRequest(http.MethodGet, "/custom", http.NoBody)
+	w := httptest.NewRecorder()
+
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, "public, max-age=60", w.Header().Get("Cache-Control"))
+}