Add webhook templating (#23289)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

spec/lib/webhooks/payload_renderer_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Webhooks::PayloadRenderer do
+  subject(:renderer) { described_class.new(json) }
+
+  let(:event)   { Webhooks::EventPresenter.new(type, object) }
+  let(:payload) { ActiveModelSerializers::SerializableResource.new(event, serializer: REST::Admin::WebhookEventSerializer, scope: nil, scope_name: :current_user).as_json }
+  let(:json)    { Oj.dump(payload) }
+
+  describe '#render' do
+    context 'when event is account.approved' do
+      let(:type)   { 'account.approved' }
+      let(:object) { Fabricate(:account, display_name: 'Foo"') }
+
+      it 'renders event-related variables into template' do
+        expect(renderer.render('foo={{event}}')).to eq 'foo=account.approved'
+      end
+
+      it 'renders event-specific variables into template' do
+        expect(renderer.render('foo={{object.username}}')).to eq "foo=#{object.username}"
+      end
+
+      it 'escapes values for use in JSON' do
+        expect(renderer.render('foo={{object.account.display_name}}')).to eq 'foo=Foo\\"'
+      end
+    end
+  end
+end