How Single Sign-On (SSO) Simplifies Access Across Multiple Apps

Single Sign-On (SSO) is an authentication mechanism that allows a user to log in once and then access multiple independent software systems without re‑entering credentials. After a successful login, a trusted session is shared among all participating applications.

Core SSO Architecture

A typical SSO setup includes the following roles:

CAS Server (Authentication Server) : Handles primary credential verification, supports multi‑factor authentication, issues tickets (TGT, ST), and implements protocols such as CAS v1/v2/v3, SAML, and OAuth2/OpenID Connect.

Service Providers / Clients : Applications that redirect unauthenticated users to the CAS server, validate tickets, and create local sessions based on the authentication result.

Browser : Carries the CAS server cookie across different domain names, preserving the unified login state.

Auxiliary Components : Reverse proxy/load balancer for high availability, logging/auditing for security events, cache (e.g., Redis) for ticket and session storage, and optional MFA/SSO extensions.

CAS Server Details

The CAS server provides core functions such as credential validation, ticket generation and management, protocol support, and single‑sign‑out coordination. It creates a Ticket‑Granting Ticket (TGT) after successful login and issues Service Tickets (ST) for individual service requests.

Service Provider Logic

When a user accesses an application without a local session, the service redirects the browser to the CAS login URL (e.g., cas.com/login?service=appA.com). After authentication, the CAS server redirects back with an ST (e.g., appA.com?ticket=ST‑xxxx). The application then validates the ST with the CAS server via a server‑to‑server call, establishes its own session, and grants access.

SSO Flow

The process consists of a front‑end redirect and a back‑end verification:

User attempts to access appA.com and finds no local session.

App A redirects the browser to the CAS login page.

User logs in on the CAS page.

CAS creates a TGT and issues an ST, then redirects back to appA.com?ticket=ST‑xxxx.

App A validates the ST with the CAS server.

Upon successful validation, App A creates a local session and the user gains access.

Illustrative Diagram

┌────────────┐
│ Browser   │
└─────┬──────┘
      │
┌─────▼──────┐
│ System A   │   CAS Client
│   A        │
└─────┬──────┘
      │
   Redirect
      │
┌─────▼──────┐
│ CAS Server │   Authentication Server
│   (Auth)   │
└─────┬──────┘
      │
   ┌──▼───┐
   │System B│   CAS Client
   │   B   │
   └───────┘
└────────────┘

This diagram shows the interaction between the browser, two service systems (A and B), and the central CAS server during the SSO process.