Support third-party checkout confirmation

Orders and subscriptions created by untrusted apps are confirmed by the
user on Anikeen ID. confirmationUrl($returnUrl) on Order and
Subscription builds the link with the return URL; checking out such a
draft throws ConfirmationRequiredException carrying the same URL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/Id/CheckoutConfirmationTest.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Anikeen\Id\Tests;
+
+use Anikeen\Id\Billable;
+use Anikeen\Id\Exceptions\ConfirmationRequiredException;
+use Illuminate\Database\Eloquent\Model;
+
+class CheckoutConfirmationTest extends TestCase
+{
+    private function owner(): Model
+    {
+        $owner = new class extends Model {
+            use Billable;
+
+            protected $guarded = [];
+        };
+        $owner->anikeen_id = '01JUSER';
+        $owner->anikeen_id_access_token = 'user-token';
+
+        return $owner;
+    }
+
+    public function test_a_draft_order_links_to_its_confirmation_with_the_return_url(): void
+    {
+        $this->respond(200, ['data' => []]); // orders() loads the list first
+        $this->respond(201, ['data' => ['id' => '01JORD', 'status' => 'draft', 'confirmation_url' => 'https://id.anikeen.com/checkout/orders/01JORD']]);
+
+        $order = $this->owner()->orders()->create(['billing_address_id' => '01JADDR', 'items' => []]);
+
+        $this->assertSame('https://id.anikeen.com/checkout/orders/01JORD', $order->confirmationUrl());
+        $this->assertSame(
+            'https://id.anikeen.com/checkout/orders/01JORD?return_url=https%3A%2F%2Fshop.test%2Fdone%3Fcart%3D1',
+            $order->confirmationUrl('https://shop.test/done?cart=1'),
+        );
+        $this->assertSame('POST /api/v1/orders', $this->sent[1]['request']->getMethod() . ' ' . $this->sent[1]['request']->getUri()->getPath());
+    }
+
+    public function test_checked_out_bookings_have_no_confirmation_url(): void
+    {
+        $this->respond(200, ['data' => []]);
+        $this->respond(201, ['data' => ['id' => '01JORD', 'status' => 'completed', 'confirmation_url' => null]]);
+
+        $this->assertNull($this->owner()->orders()->create([])->confirmationUrl('https://shop.test/done'));
+    }
+
+    public function test_checking_out_a_draft_as_a_third_party_app_points_to_the_confirmation(): void
+    {
+        $this->respond(200, ['data' => []]); // subscriptions() loads the list first
+        $this->respond(201, ['data' => ['id' => '01JSUB', 'active' => false, 'confirmation_url' => 'https://id.anikeen.com/checkout/subscriptions/01JSUB']]);
+        $this->respond(403, ['message' => 'The user has to confirm this on Anikeen ID.', 'error' => 'confirmation_required', 'confirmation_url' => 'https://id.anikeen.com/checkout/subscriptions/01JSUB']);
+
+        $subscription = $this->owner()->subscriptions()->create(['name' => 'Pro', 'unit' => 'month', 'price' => 4.99]);
+
+        try {
+            $subscription->checkout();
+            $this->fail('Expected a ConfirmationRequiredException.');
+        } catch (ConfirmationRequiredException $e) {
+            $this->assertSame(403, $e->getCode());
+            $this->assertSame('https://id.anikeen.com/checkout/subscriptions/01JSUB', $e->confirmationUrl);
+        }
+    }
+}