I need to add a messaging option to my website. I already have a Slack account. I would like to integrate Slack so that when a user clicks on the chat option, their Slack channel opens where they can send and receive messages.

Specifically, I am looking for guidance on:

1. Creating a Slack app and obtaining necessary credentials.
2. Setting up a Slack bot or integration to handle messaging.
3. Implementing the integration in PHP to open the user’s Slack channel.
4. Handling authentication and ensuring secure communication.

Any examples, code snippets, or detailed steps would be greatly appreciated. Thank you!