Add signal for required pre-checkout confirmations

doc/development/api/general.rst

@@ -25,7 +25,7 @@ Frontend
 --------
 
 .. automodule:: pretix.presale.signals
-   :members: html_head, footer_links, front_page_top, front_page_bottom
+   :members: html_head, footer_links, front_page_top, front_page_bottom, checkout_confirm_messages
 
 
 .. automodule:: pretix.presale.signals

src/pretix/presale/checkoutflow.py

@@ -2,7 +2,7 @@ from django.conf import settings
 from django.contrib import messages
 from django.core.exceptions import ValidationError
 from django.core.validators import EmailValidator
-from django.http import HttpResponseNotAllowed
+from django.http import HttpResponseNotAllowed, JsonResponse
 from django.shortcuts import redirect
 from django.utils import translation
 from django.utils.functional import cached_property
@@ -15,7 +15,9 @@ from pretix.base.services.orders import perform_order
 from pretix.base.signals import register_payment_providers
 from pretix.multidomain.urlreverse import eventreverse
 from pretix.presale.forms.checkout import ContactForm, InvoiceAddressForm
-from pretix.presale.signals import checkout_flow_steps, order_meta_from_request
+from pretix.presale.signals import (
+    checkout_confirm_messages, checkout_flow_steps, order_meta_from_request,
+)
 from pretix.presale.views import CartMixin, get_cart_total
 from pretix.presale.views.async import AsyncAction
 from pretix.presale.views.questions import QuestionsViewMixin
@@ -307,8 +309,17 @@ class ConfirmStep(CartMixin, AsyncAction, TemplateFlowStep):
         ctx['payment'] = self.payment_provider.checkout_confirm_render(self.request)
         ctx['payment_provider'] = self.payment_provider
         ctx['addr'] = self.invoice_address
+        ctx['confirm_messages'] = self.confirm_messages
         return ctx
 
+    @cached_property
+    def confirm_messages(self):
+        msgs = {}
+        responses = checkout_confirm_messages.send(self.request.event)
+        for receiver, response in responses:
+            msgs.update(response)
+        return msgs
+
     @cached_property
     def payment_provider(self):
         responses = register_payment_providers.send(self.request.event)
@@ -335,6 +346,20 @@ class ConfirmStep(CartMixin, AsyncAction, TemplateFlowStep):
 
     def post(self, request):
         self.request = request
+
+        if self.confirm_messages:
+            for key, msg in self.confirm_messages.items():
+                if request.POST.get('confirm_{}'.format(key)) != 'yes':
+                    msg = str(_('You need to check all checkboxes on the bottom of the page.'))
+                    messages.error(self.request, msg)
+                    if "ajax" in self.request.POST or "ajax" in self.request.GET:
+                        return JsonResponse({
+                            'ready': True,
+                            'redirect': self.get_error_url(),
+                            'message': msg
+                        })
+                    return redirect(self.get_error_url())
+
         meta_info = {}
         for receiver, response in order_meta_from_request.send(sender=request.event, request=request):
             meta_info.update(response)

src/pretix/presale/signals.py

@@ -21,6 +21,16 @@ are expected to return a dictionary containing the keys ``label`` and ``url``.
 As with all plugin signals, the ``sender`` keyword argument will contain the event.
 """
 
+checkout_confirm_messages = EventPluginSignal()
+"""
+This signal is sent out to retrieve short messages that need to be acknowledged by the user before the
+order can be completed. This is typically used for something like "accept the terms and conditions".
+Receivers are expected to return a dictionary where the keys are globally unique identifiers for the
+message and the values can be arbitrary HTML.
+
+As with all plugin signals, the ``sender`` keyword argument will contain the event.
+"""
+
 checkout_flow_steps = EventPluginSignal()
 """
 This signal is sent out to retrieve pages for the checkout flow

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

@@ -115,6 +115,25 @@
                 </div>
             </div>
         </div>
+        {% if confirm_messages %}
+            <div class="panel panel-primary panel-contact">
+                <div class="panel-heading">
+                    <h3 class="panel-title">
+                        {% trans "Confirmations" %}
+                    </h3>
+                </div>
+                <div class="panel-body">
+                    {% for key, desc in confirm_messages.items %}
+                        <div class="checkbox">
+                            <label>
+                                <input type="checkbox" class="checkbox" value="yes" name="confirm_{{ key }}" required>
+                                {{ desc|safe }}
+                            </label>
+                        </div>
+                    {% endfor %}
+                </div>
+            </div>
+        {% endif %}
         <div class="row checkout-button-row clearfix">
             <div class="col-md-4">
                 <a class="btn btn-block btn-default btn-lg"

src/pretix/presale/views/event.py

@@ -14,6 +14,7 @@ from django.views.generic import TemplateView
 
 from pretix.base.models import ItemVariation
 from pretix.multidomain.urlreverse import eventreverse
+
 from . import CartMixin, EventViewMixin
 
 SessionStore = import_module(settings.SESSION_ENGINE).SessionStore