The text outlines a tutorial on updating a legacy PHP business application to use a modern authentication system, specifically transitioning to OAuth with FusionAuth. The legacy application, humorously nicknamed "The ATM" due to its profitability, originally uses a homegrown authentication system that presents integration challenges and maintenance burdens. The guide details the setup process for FusionAuth, including application and user configuration, and demonstrates how to integrate an OAuth library using Composer to manage dependencies. The process involves replacing local authentication logic with FusionAuth's OAuth flow, enhancing security and centralizing user management. The tutorial highlights the benefits of centralized authentication, such as streamlined user administration and reduced security risks, while also hinting at an upcoming guide on migrating existing user data to the new system.