Make "Show in backend" button on ticket pages available on custom domains (#4743)

src/pretix/presale/views/order.py

@@ -60,6 +60,7 @@ from django.utils.translation import gettext, gettext_lazy as _
 from django.views.decorators.clickjacking import xframe_options_exempt
 from django.views.generic import ListView, TemplateView, View
 
+from pretix.base.auth import has_event_access_permission
 from pretix.base.models import (
     CachedTicket, Checkin, GiftCard, Invoice, Order, OrderPosition, Quota,
     TaxRule,
@@ -205,10 +206,8 @@ class TicketPageMixin:
 
         ctx['download_buttons'] = self.download_buttons
 
-        ctx['backend_user'] = (
-            self.request.user.is_authenticated
-            and self.request.user.has_event_permission(self.request.organizer, self.request.event, 'can_view_orders', request=self.request)
-        )
+        ctx['backend_user'] = has_event_access_permission(self.request, 'can_view_orders')
+
         return ctx
 
     @cached_property