first commit

backend/internal/server/middleware/security_headers.go

@@ -0,0 +1,26 @@
+package middleware
+
+import (
+	"strings"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/gin-gonic/gin"
+)
+
+// SecurityHeaders sets baseline security headers for all responses.
+func SecurityHeaders(cfg config.CSPConfig) gin.HandlerFunc {
+	policy := strings.TrimSpace(cfg.Policy)
+	if policy == "" {
+		policy = config.DefaultCSPPolicy
+	}
+
+	return func(c *gin.Context) {
+		c.Header("X-Content-Type-Options", "nosniff")
+		c.Header("X-Frame-Options", "DENY")
+		c.Header("Referrer-Policy", "strict-origin-when-cross-origin")
+		if cfg.Enabled {
+			c.Header("Content-Security-Policy", policy)
+		}
+		c.Next()
+	}
+}