Guide: Build a Self-Hosted SSO System Using Laravel 12 and Passport v13

A new hands-on technical guide walks developers through building a self-hosted Single Sign-On system using Laravel 12 and Passport v13, without relying on third-party identity providers like Google, Auth0, or Keycloak. The setup involves a Central Portal acting as an OAuth 2.0 Authorization Server that owns the users table and issues tokens, while multiple child sites delegate all authentication to it. The guide uses the Authorization Code grant type, considered the only secure flow for server-rendered web applications, ensuring access tokens never reach the browser. Key design decisions include no consent screen for first-party apps, binary per-site permissions, and manual user provisioning with email as the join key between the portal and child sites. The tutorial is structured to be buildable on a fresh Laravel install, covering system architecture, authentication workflows, end-to-end testing, and security considerations.