Improve outbound URL validation

tests/Unit/NotificationWebhookSafetyTest.php

@@ -0,0 +1,36 @@
+<?php
+
+use App\Jobs\SendMessageToDiscordJob;
+use App\Jobs\SendMessageToSlackJob;
+use App\Notifications\Dto\DiscordMessage;
+use App\Notifications\Dto\SlackMessage;
+use Illuminate\Support\Facades\Http;
+use Tests\TestCase;
+
+uses(TestCase::class);
+
+it('blocks queued Slack notifications to IPv4-mapped link-local URLs', function () {
+    Http::fake();
+
+    $job = new SendMessageToSlackJob(
+        new SlackMessage('Test', 'Description'),
+        'http://[::ffff:169.254.169.254]/'
+    );
+
+    $job->handle();
+
+    Http::assertNothingSent();
+});
+
+it('blocks queued Discord notifications to IPv4-mapped link-local URLs', function () {
+    Http::fake();
+
+    $job = new SendMessageToDiscordJob(
+        new DiscordMessage('Test', 'Description', DiscordMessage::infoColor()),
+        'http://[::ffff:169.254.169.254]/'
+    );
+
+    $job->handle();
+
+    Http::assertNothingSent();
+});