Add API endpoint for default fixed metadata variables of JSON dump plugin

src/openapi.yaml

@@ -3800,6 +3800,34 @@ paths:
               $ref: '#/components/headers/X-Is-Form-Designer'
             Content-Language:
               $ref: '#/components/headers/Content-Language'
+  /api/v2/registration/plugins/json-dump/fixed-metadata-variables:
+    get:
+      operationId: registration_plugins_json_dump_fixed_metadata_variables_retrieve
+      description: Return a list of fixed metadata variables for the JSON dump registration
+        backend that are needed by the frontend as default options.
+      summary: Fixed metadata variables JSON dump registration backend
+      tags:
+      - registration
+      security:
+      - tokenAuth: []
+      - cookieAuth: []
+      - {}
+      responses:
+        '200':
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/FixedMetadataVariable'
+          description: ''
+          headers:
+            X-Session-Expires-In:
+              $ref: '#/components/headers/X-Session-Expires-In'
+            X-CSRFToken:
+              $ref: '#/components/headers/X-CSRFToken'
+            X-Is-Form-Designer:
+              $ref: '#/components/headers/X-Is-Form-Designer'
+            Content-Language:
+              $ref: '#/components/headers/Content-Language'
   /api/v2/registration/plugins/objects-api/target-paths:
     post:
       operationId: registration_plugins_objects_api_target_paths_create
@@ -7477,6 +7505,27 @@ components:
       - code
       - name
       - reason
+    FixedMetadataVariable:
+      type: object
+      properties:
+        variables:
+          type: array
+          items:
+            type: string
+            pattern: ^(\w|\w[\w.\-]*\w)$
+          readOnly: true
+          default:
+          - public_reference
+          - form_name
+          - form_version
+          - form_id
+          - registration_timestamp
+          - auth_type
+          title: Fixed metadata variable key list
+          description: A list of fixed variables to use in the metadata. These include
+            the registration variables of the JSON dump plugin.
+      required:
+      - variables
     Form:
       type: object
       description: |-

src/openforms/js/components/admin/form_design/constants.js

@@ -4,6 +4,8 @@ export const REGISTRATION_BACKENDS_ENDPOINT = '/api/v2/registration/plugins';
 export const OBJECTS_API_OBJECTTYPES_ENDPOINT = '/api/v2/objects-api/object-types';
 export const REGISTRATION_OBJECTS_TARGET_PATHS =
   '/api/v2/registration/plugins/objects-api/target-paths';
+export const REGISTRATION_JSON_DUMP_FIXED_METADATA_VARIABLES =
+  '/api/v2/registration/plugins/json-dump/fixed-metadata-variables';
 export const AUTH_PLUGINS_ENDPOINT = '/api/v2/authentication/plugins';
 export const PREFILL_PLUGINS_ENDPOINT = '/api/v2/prefill/plugins';
 export const DMN_PLUGINS_ENDPOINT = '/api/v2/dmn/plugins';

src/openforms/js/components/admin/form_design/registrations/json_dump/JSONDumpOptionsForm.js

@@ -1,14 +1,17 @@
 import PropTypes from 'prop-types';
 import React, {useContext} from 'react';
 import {FormattedMessage} from 'react-intl';
+import {useAsync} from 'react-use';
 
+import {REGISTRATION_JSON_DUMP_FIXED_METADATA_VARIABLES} from 'components/admin/form_design/constants';
 import Fieldset from 'components/admin/forms/Fieldset';
 import ModalOptionsConfiguration from 'components/admin/forms/ModalOptionsConfiguration';
 import {
   ValidationErrorContext,
   ValidationErrorsProvider,
   filterErrors,
 } from 'components/admin/forms/ValidationErrors';
+import {get} from 'utils/fetch';
 import {getChoicesFromSchema} from 'utils/json-schema';
 
 import {
@@ -29,6 +32,15 @@ const JSONDumpOptionsForm = ({name, label, schema, formData, onChange}) => {
     ([value, label]) => ({value, label})
   );
 
+  // Get fixed metadata variables
+  const {value: fixedMetadataVariables} = useAsync(async () => {
+    const response = await get(REGISTRATION_JSON_DUMP_FIXED_METADATA_VARIABLES);
+    if (!response.ok) {
+      throw new Error(response.statusText);
+    }
+    return response.data;
+  }, []);
+
   return (
     <ModalOptionsConfiguration
       name={name}
@@ -44,7 +56,7 @@ const JSONDumpOptionsForm = ({name, label, schema, formData, onChange}) => {
         service: null,
         path: '',
         variables: [],
-        fixedMetadataVariables: [],
+        fixedMetadataVariables: fixedMetadataVariables || [],
         additionalMetadataVariables: [],
         ...formData,
       }}

src/openforms/js/components/admin/form_design/registrations/json_dump/JSONDumpSummaryHandler.js

@@ -5,10 +5,10 @@ import {FormattedMessage} from 'react-intl';
 import {IconNo, IconYes} from 'components/admin/BooleanIcons';
 
 const JSONDumpSummaryHandler = ({variable, backendOptions}) => {
-  const isIncludedInVariables = backendOptions.variables.includes(variable.key);
+  const isIncludedInVariables = backendOptions.variables?.includes(variable.key);
   const isIncludedInMetadata =
-    backendOptions.fixedMetadataVariables.includes(variable.key) ||
-    backendOptions.additionalMetadataVariables.includes(variable.key);
+    backendOptions.fixedMetadataVariables?.includes(variable.key) ||
+    backendOptions.additionalMetadataVariables?.includes(variable.key);
 
   return (
     <>

src/openforms/registrations/api/urls.py

@@ -23,4 +23,8 @@
         "plugins/zgw-api/",
         include("openforms.registrations.contrib.zgw_apis.api.urls"),
     ),
+    path(
+        "plugins/json-dump/",
+        include("openforms.registrations.contrib.json_dump.api.urls"),
+    ),
 ]

src/openforms/registrations/contrib/json_dump/api/serializers.py

@@ -0,0 +1,25 @@
+from django.utils.translation import gettext_lazy as _
+
+from rest_framework import serializers
+
+from openforms.formio.api.fields import FormioVariableKeyField
+
+
+class FixedMetadataVariableSerializer(serializers.Serializer):
+    variables = serializers.ListField(
+        child=FormioVariableKeyField(),
+        label=_("Fixed metadata variable key list"),
+        help_text=_(
+            "A list of fixed variables to use in the metadata. These include the "
+            "registration variables of the JSON dump plugin."
+        ),
+        default=[
+            "public_reference",
+            "form_name",
+            "form_version",
+            "form_id",
+            "registration_timestamp",
+            "auth_type",
+        ],
+        read_only=True,
+    )

src/openforms/registrations/contrib/json_dump/api/urls.py

@@ -0,0 +1,13 @@
+from django.urls import path
+
+from .views import FixedMetadataVariablesView
+
+app_name = "registrations_json_dump"
+
+urlpatterns = [
+    path(
+        "fixed-metadata-variables",
+        FixedMetadataVariablesView.as_view(),
+        name="fixed_metadata_variables",
+    )
+]

src/openforms/registrations/contrib/json_dump/api/views.py

@@ -0,0 +1,24 @@
+from django.utils.translation import gettext_lazy as _
+
+from drf_spectacular.utils import extend_schema
+from rest_framework.response import Response
+from rest_framework.views import APIView
+
+from .serializers import FixedMetadataVariableSerializer
+
+
+class FixedMetadataVariablesView(APIView):
+
+    serializer_class = FixedMetadataVariableSerializer
+
+    @extend_schema(
+        summary=_("Fixed metadata variables JSON dump registration backend"),
+        description=_(
+            "Return a list of fixed metadata variables for the JSON dump registration "
+            "backend that are needed by the frontend as default options."
+        ),
+    )
+    def get(self, request, *args, **kwargs):
+        serializer = self.serializer_class(data={})
+        serializer.is_valid()
+        return Response(serializer.data["variables"])

src/openforms/registrations/contrib/json_dump/config.py

@@ -47,26 +47,19 @@ class JSONDumpOptionsSerializer(JsonSchemaSerializerMixin, serializers.Serialize
         required=True,
         min_length=1,
     )
-    # Note: this field cannot be updated in the frontend, and is used as read-only.
-    #  Adding a read_only=True argument to it, though, will make it not available in the
-    #  backend options of the plugin, as they are not added to the validated_data
-    #  property of the serializer.
+    # Note: the defaults for this field are listed in
+    # `.api.views.FixedMetadataVariableSerializer`. They are in a separate API to make
+    # them available in the frontend as default fixed options.
+    # TODO: this list should be validated against the available FormVariable records
+    #  that exist for the form.
     fixed_metadata_variables = serializers.ListField(
         child=FormioVariableKeyField(),
-        default=[
-            "public_reference",
-            "form_name",
-            "form_version",
-            "form_id",
-            "registration_timestamp",
-            "auth_type",
-        ],
         label=_("Fixed metadata variable key list"),
         help_text=_(
             "A list of required variables to use in the metadata. These include "
             "the registration variables of the JSON dump plugin."
         ),
-        required=False,
+        required=True,
     )
     # TODO: this list should be validated against the available FormVariable records
     #  that exist for the form.

src/openforms/registrations/contrib/json_dump/tests/test_api.py

@@ -0,0 +1,13 @@
+from django.test import TestCase
+from django.urls import reverse_lazy
+
+
+class JSONDumpAPITests(TestCase):
+
+    endpoint = reverse_lazy("api:registrations_json_dump:fixed_metadata_variables")
+
+    def test_get(self):
+        response = self.client.get(self.endpoint)
+
+        self.assertEqual(response.status_code, 200)
+        self.assertTrue(isinstance(response.json(), list))