Fix #1102 -- "View in backend" (doesn't work with custom domains)

src/pretix/presale/templates/pretixpresale/event/order.html

@@ -47,6 +47,11 @@
         {% if order.testmode %}
             <span class="label label-warning">{% trans "TEST MODE" %}</span>
         {% endif %}
+        {% if backend_user %}
+            <a href="{% url "control:event.order" event=request.event.slug organizer=request.organizer.slug code=order.code %}" class="btn btn-default">
+                {% trans "View in backend" %}
+            </a>
+        {% endif %}
         {% include "pretixpresale/event/fragment_order_status.html" with order=order class="pull-right" %}
         <div class="clearfix"></div>
     </h2>

src/pretix/presale/views/order.py

@@ -128,6 +128,11 @@ class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TemplateView):
             self.order.total != Decimal('0.00') or not self.request.event.settings.invoice_address_not_asked_free
         )
 
+        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)
+        )
+
         if self.order.status == Order.STATUS_PENDING:
             ctx['pending_sum'] = self.order.pending_sum