Initial

backend/internal/csrf/middleware.go

@@ -0,0 +1,51 @@
+package csrf
+
+import (
+	"context"
+	"crypto/subtle"
+	"log/slog"
+	"net/http"
+)
+
+const CsrfKey = "csrf"
+const CsrfLength = 32
+
+func NewMiddleware(cookieName, formName string, secure bool) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			cookie, err := r.Cookie(cookieName)
+			var cookieValue string
+
+			if err != nil || cookie.Value == "" {
+				cookieValue, err = UpdateCsrf(w, cookieName, secure)
+				if err != nil {
+					slog.Error("update csrf", slog.String("op", "middleware.UpdateCsrf"), slog.Any("error", err))
+					http.Error(w, "Internal server error", http.StatusInternalServerError)
+					return
+				}
+			} else {
+				cookieValue = cookie.Value
+			}
+
+			ctx := context.WithValue(r.Context(), CsrfKey, cookieValue)
+			r = r.WithContext(ctx)
+
+			if r.Method == http.MethodGet || r.Method == http.MethodHead || r.Method == http.MethodOptions {
+				next.ServeHTTP(w, r)
+				return
+			}
+
+			formValue := r.FormValue(formName)
+			if formValue == "" {
+				formValue = r.Header.Get("X-CSRF-Token")
+			}
+
+			if subtle.ConstantTimeCompare([]byte(formValue), []byte(cookieValue)) != 1 {
+				http.Error(w, "CSRF Token Validation Failed", http.StatusForbidden)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}