Laravel broadcasting with SNS

bootstrap.php

<?php

// standard bootstrap stuff

app('Illuminate\Broadcasting\BroadcastManager')->extend('sns', function ($app, $config) {
    return new SnsBroadcaster($app['Aws\Sns\SnsClient'], [
        'channel-name' => 'arn:aws:sns:us-east-1:698519295917:My-Topic'    
    ]);
});

SnsBroadcaster.php

<?php

use Aws\Sns\SnsClient;
use Illuminate\Contracts\Broadcasting\Broadcaster;

class SnsBroadcaster implements Broadcaster
{
    /** @var SnsClient */
    private $sns;
    /** @var array */
    private $channelMapping;

    public function __construct(SnsClient $client, array $channelMapping)
    {
        $this->sns = $client;
        $this->channelMapping = $channelMapping;
    }

    public function broadcast(array $channels, $event, array $payload = [])
    {
        $payload = json_encode(['event' => $event, 'data' => $payload]);

        foreach ($channels as $channel) {
            $this->sns->publish([
                'Message' => $payload,
                'TopicArn' => array_get($this->channelMapping, $channel),
            ]);
        }
    }
}