🐛 [#4103] Use the plugin appointment ID instead of our internal DB pk

Appointment details were being retrieved using our internal database primary key,
but that looks up records from the appointment system that are unlikely to
match with the actual appointment ID recorded for a given appointment.

Backport-of: #4108

src/openforms/appointments/renderer.py

@@ -45,8 +45,9 @@ def __str__(self) -> SafeString:
         )
         plugin = get_plugin(plugin=appointment.plugin)
 
+        identifier: str = self.submission.appointment_info.appointment_id
         ctx = {
-            "appointment": plugin.get_appointment_details(appointment.pk),
+            "appointment": plugin.get_appointment_details(identifier),
             "contact_details": self.get_children(),  # todo: a bit of a wart
         }
         return render_to_string(template_name, ctx)

src/openforms/appointments/tests/test_pdf.py

@@ -1,10 +1,13 @@
-from django.test import RequestFactory, TestCase, override_settings
+from unittest.mock import patch
+
+from django.test import RequestFactory, TestCase, override_settings, tag
 from django.utils.html import escape
 
 from openforms.accounts.tests.factories import SuperUserFactory
 from openforms.submissions.dev_views import SubmissionPDFTestView
 from openforms.submissions.tests.factories import SubmissionFactory
 
+from ..contrib.demo.plugin import DemoAppointment
 from .factories import AppointmentFactory, AppointmentProductFactory
 
 
@@ -18,6 +21,7 @@ def setUpTestData(cls):
             submission__registration_success=True,
             submission__with_report=True,
             appointment_info__registration_ok=True,
+            appointment_info__appointment_id="a-remote-id",
             location__identifier="1",
         )
         AppointmentProductFactory.create(
@@ -59,3 +63,17 @@ def test_submission_without_appointment_shows_no_appointment_info(self):
         html = submission.report.generate_submission_report_pdf()
 
         self.assertNotIn("Afspraakinformatie", html)
+
+    @tag("gh-4103")
+    def test_uses_remote_appoinment_id(self):
+        plugin = DemoAppointment("demo")
+
+        with (
+            patch("openforms.appointments.renderer.get_plugin", return_value=plugin),
+            patch.object(
+                plugin, "get_appointment_details", wraps=plugin.get_appointment_details
+            ) as m_get_details,
+        ):
+            self.submission.report.generate_submission_report_pdf()
+
+        m_get_details.assert_called_once_with("a-remote-id")