DEV: Add modifier for webhook event header generation (#27054)

app/jobs/regular/emit_web_hook_event.rb

@@ -45,7 +45,15 @@ module Jobs
       web_hook_body = build_webhook_body
       web_hook_event = create_webhook_event(web_hook_body)
       uri = URI(@web_hook.payload_url.strip)
+
       web_hook_headers = build_webhook_headers(uri, web_hook_body, web_hook_event)
+      web_hook_headers =
+        DiscoursePluginRegistry.apply_modifier(
+          :web_hook_event_headers,
+          web_hook_headers,
+          web_hook_body,
+          web_hook_event,
+        )
 
       emitter = WebHookEmitter.new(@web_hook, web_hook_event)
       web_hook_response = emitter.emit!(headers: web_hook_headers, body: web_hook_body)

spec/jobs/emit_web_hook_event_spec.rb

@@ -345,5 +345,37 @@ RSpec.describe Jobs::EmitWebHookEvent do
       )
       expect(event.payload).to eq(MultiJson.dump(ping: "OK"))
     end
+
+    context "with `webhook_event_headers` modifier" do
+      let(:modifier_block) do
+        Proc.new do |headers, _, _|
+          headers["D-Test-Woo"] = "xyz"
+          headers
+        end
+      end
+      it "Allows for header modifications" do
+        plugin_instance = Plugin::Instance.new
+        plugin_instance.register_modifier(:web_hook_event_headers, &modifier_block)
+
+        stub_request(:post, post_hook.payload_url).to_return(body: "OK", status: 200)
+
+        topic_event_type = WebHookEventType.all.first
+        web_hook_id = Fabricate("#{topic_event_type.name.gsub("_created", "")}_web_hook").id
+
+        job.execute(
+          web_hook_id: web_hook_id,
+          event_type: topic_event_type.name,
+          payload: { test: "some payload" }.to_json,
+        )
+        webhook_event = WebHookEvent.last
+        expect(JSON.parse(webhook_event.headers)).to include("D-Test-Woo" => "xyz")
+      ensure
+        DiscoursePluginRegistry.unregister_modifier(
+          plugin_instance,
+          :web_hook_event_headers,
+          &modifier_block
+        )
+      end
+    end
   end
 end