Add WebHook connection callback

app/Client/Callbacks/WebHookConnectionCallback.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Client\Callbacks;
+
+use App\Server\Connections\ControlConnection;
+use Clue\React\Buzz\Browser;
+
+class WebHookConnectionCallback
+{
+    /** @var Browser  */
+    protected $browser;
+
+    public function __construct(Browser $browser)
+    {
+        $this->browser = $browser;
+    }
+
+    public function handle(ControlConnection $connection)
+    {
+        $this->browser->post(config('expose.admin.connection_callbacks.webhook.url'), [
+            'Content-Type' => 'application/json',
+            'Accept' => 'application/json',
+            'X-Signature' => $this->generateWebhookSigningSecret($connection),
+        ], json_encode($connection->toArray()));
+    }
+
+    protected function generateWebhookSigningSecret(ControlConnection $connection)
+    {
+        return hash_hmac('sha256', $connection->client_id, config('expose.admin.connection_callbacks.webhook.secret'));
+    }
+}