Single Sign-On (SSO) Explained Simply

SSO allows users to authenticate with a single username and password to access multiple connected applications or services. It acts as a central authentication gatekeeper.

Today, you see SSO implemented in consumer apps as the “Sign In With Google” or “Sign In With Apple” buttons. Logging into your Gmail grants you SSO access to other Google services like YouTube, Google Drive, etc. Furthermore, many companies use SSO for accessing internal systems, email, and software tools.

How SSO Works

SSO works by establishing a central authentication server that all participating applications trust. When a user attempts to access an application, the process typically follows these steps:

  1. Authentication Request: The user accesses the first application.
  2. SSO Redirect: If not already authenticated, the application redirects the user to the SSO server.
  3. Login: The user logs in with their central credentials.
  4. Authentication Token: The SSO server authenticates the user, generates an authentication token, and sends it back to the user’s browser.
  5. Token Validation: The user’s browser presents this token to the application, which validates it with the SSO server.
  6. Access Granted: Once validated, the application grants access to the user. For subsequent applications, steps 2-5 are bypassed or significantly simplified, as the user’s authentication status can be shared securely.

Advantages of SSO

  • Enhanced User Experience: SSO simplifies the user’s login process across multiple applications, reducing password fatigue and streamlining access.
  • Reduced IT Costs: It decreases the need for IT intervention due to password-related issues, lowering support costs.
  • Improved Security: Centralizing authentication can enhance security, provided the SSO solution is robustly implemented and managed. It allows for consistent application of security policies.
  • Compliance and Reporting: SSO makes it easier to monitor and manage access across applications, aiding in compliance with security standards.

Challenges of SSO

  • Single Point of Failure: If the SSO system experiences a failure, it could prevent access to all connected applications.
  • Security Risks: While SSO can improve security, it also means that if a user’s credentials are compromised, the attacker could gain access to all applications accessible via the SSO system.
  • Implementation Complexity: Integrating SSO with all applications, especially legacy systems, can be complex and resource-intensive.

Implementation Strategies

  1. SAML (Security Assertion Markup Language): An open standard for exchanging authentication and authorization data between parties, especially between an identity provider and a service provider.
  2. OAuth and OpenID Connect: OAuth is an authorization framework that allows third-party services to exchange web resources on behalf of a user. OpenID Connect (OIDC) is built on top of OAuth 2.0 and adds an authentication layer, allowing apps to verify the user’s identity.
  3. Custom SSO Solutions: Some organizations may develop custom SSO solutions tailored to their specific infrastructure.


Integrating Google Sign-In into your web app