In order to make webhooks work easily with Slack, i have added this line of code in ‘modules/Cockpit/webhooks.php’
Slack payload expect a text attribute otherwise it send a http 400
$data = json_encode([ 'event' => $evt, 'hook' => $webhook['name'], 'backend' => COCKPIT_ADMIN, 'args' => func_get_args(), 'text' => $webhook['name'] ]);
Feel free to change the implementation if you guys thinks it is great idea.
What would be nice is to have a list of attributes/values added in the webhooks setting so we could add attributes dynamically.