02. Single Sign-On (SSO)

0 March 18, 2025

Introduction

Single Sign-On (SSO) is an authentication method that allows a user to access multiple applications or systems with one set of login credentials. This increases usability and security, as users have to remember fewer passwords and IT departments have to resolve fewer password-related issues.

How does SSO work?

SSO works by using a trusted Identity Provider (IdP) to authenticate users. When a user logs into an application (Service Provider), they are redirected to the IdP, which validates their identity. After successful authentication, a token or session is generated, allowing the user to access other linked applications without logging in again.

Step-by-step process:
  1. The user tries to access an application (Service Provider).
  2. The application redirects the user to the Identity Provider (IdP).
  3. The user logs in at the IdP.
  4. The IdP verifies the identity and sends an authentication token back to the application.
  5. The user gains access to the application and can open other linked applications without logging in again.

Advantages of SSO

  • Improved user experience: Users only need to log in once.
  • Less password management: Reduces the risk of weak or reused passwords.
  • Stronger security: Access is better protected when combined with MFA.
  • Efficiency for IT: Fewer password resets and lower management costs.

Disadvantages of SSO

  • Single Point of Failure (SPoF): If the IdP fails, users cannot log in to linked applications.
  • Potential increased risk: If an account is compromised, an attacker gains access to multiple systems.

SSO protocols and standards

SSO is enabled by various protocols:

1. Security Assertion Markup Language (SAML)
  • XML-based protocol, often used in enterprise environments.
  • Popular for web applications like Google Workspace and Microsoft 365.
2. OAuth 2.0 and OpenID Connect (OIDC)
  • OAuth 2.0: An authorization protocol, often used for APIs.
  • OpenID Connect: Provides an identity layer on top of OAuth 2.0 for SSO.
  • Widely used by cloud providers and SaaS applications.
3. Kerberos
  • Network protocol used within Windows Active Directory.
  • Suitable for internal SSO within corporate networks.

Conclusion

SSO offers a balance between security and usability, provided it is well implemented. It reduces password issues and increases productivity but requires strong security measures like MFA and monitoring to minimize risks.