handler/default.go

@@ -38,6 +38,7 @@ func GetHandler(d *sql.DB, serverSettings *types.ServerSettings) http.Handler {
 	return middleware.Wrapper(
 		router,
 		middleware.Log,
+		middleware.SecFetchFilter,
 		middleware.ContentSecurityPolicy,
 		middleware.Cors(serverSettings),
 		middleware.Corp,

middleware/sec_fetch_filter.go

@@ -0,0 +1,29 @@
+package middleware
+
+import "net/http"
+
+func SecFetchFilter(next http.Handler) http.Handler {
+
+	// A map is slower than a slice, but it's easier to check if a value exists
+	allowedSites := map[string]interface{}{
+		"same-origin": nil,
+		"none":        nil,
+	}
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		secFetchSite := r.Header.Get("Sec-Fetch-Site")
+
+		if secFetchSite == "" {
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		_, exists := allowedSites[r.Header.Get("Sec-Fetch-Site")]
+		if !exists {
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		w.WriteHeader(http.StatusForbidden)
+	})
+}