Building Enterprise‑Level CAS SSO: Lessons from Our First Implementation

Why Build SSO

Before the change, each system—management backend, Jira, Confluence—had its own password, causing duplicate account creation, password‑reset overhead, and inconsistent logout behavior. The team decided to create a unified authentication solution.

Key Goals of the SSO Solution

Unified Identity: One person, one primary account recognized by all systems.

Unified Login Entry: Unauthenticated requests are redirected to a central authentication center instead of individual login pages.

Unified Logout: Logging out once at the authentication center invalidates sessions in all connected applications.

Extensible Integration: New systems can be added following a clear integration guide rather than ad‑hoc effort.

Why This Series Was Written

Many public articles explain the CAS protocol and its interfaces, but when implementing a real project the challenges shift from pure login mechanics to questions such as how third‑party systems connect, how new services are registered, where the gateway should sit, how login and logout are coordinated, and how OAuth2 and CAS cooperate.

Problems Addressed by the Series

When to use OAuth2 versus CAS for different types of applications.

The shape of credentials received by business systems (JWT from the gateway for internal services, CAS ticket for third‑party apps).

The need for a gateway to centralize authentication and API traffic.

How to achieve true single logout across all services.

System Overview

The solution consists of four core modules:

Authentication Center: Provides a unified login page, issues tickets, registers applications, and orchestrates single logout.

Gateway: Serves as the login entry point and API traffic entry for the management backend.

User Master Data Service: Stores employee accounts and normalizes login identifiers (email, employee ID, QR code) into a single user record.

Management‑Side User Service: Issues business tokens for the backend and receives logout notifications from the authentication center.

Details of why each module is designed this way are covered in the third article of the series.

Technology Stack

The entire solution is built on Java 17 using Apereo CAS, Spring Cloud Gateway, Spring Boot, and other common enterprise technologies. Specific version choices and selection rationale are explained in the architecture article.

What You’ll Be Able to Do After Reading

After completing the series, you will know the exact first steps to take when tasked with implementing SSO in your organization, whether that means examining the authentication center, modifying the gateway, or registering a new CAS service.

If a leader asks you to “integrate this new system into the unified authentication,” you will no longer be confused; you’ll understand which component to look at first.