Sellauth API Integration to WordPress Site

I already have a fully functional WordPress site and I’d like to connect it to the Sellauth.com API. My goal is to hook into the API’s endpoints so users can seamlessly interact with Sellauth without ever leaving my site. I’m open to guidance on which parts of the site should call the API first—login, checkout, dashboard, or any other template you feel is most efficient—but the final result must be cleanly coded, secure, and future-proof.

You’ll be working in a standard LAMP-based WordPress environment (PHP 8, latest WP core, custom theme). I need:

• End-to-end integration of Sellauth REST calls (authentication tokens, callbacks, error handling).
• All keys, secrets, and webhooks added through wp-config or a secure custom plugin, never hard-coded.
• Responsive front-end hooks so the user experience matches the site’s current styling.
• A short hand-off note or screen share that explains how to update or extend the integration.

Please factor in best practices for WordPress hooks, nonces, and sanitization. If you’ve connected third-party APIs via wp_remote_request or custom cURL in a plugin, you’ll feel right at home.