Single Sign-On (SSO) is an authentication mechanism that allows users to log in once and gain access to multiple applications or services without needing to authenticate again. It improves user experience and security by centralizing authentication.
How SSO Works
- User Requests Access: The user attempts to log in to an application (Service Provider - SP).
- SSO Redirects to Identity Provider (IdP): If the user is not already authenticated, they are redirected to the Identity Provider (IdP) (e.g., Google, Okta, Microsoft Azure AD).
- User Authenticates: The IdP verifies credentials (username/password, multi-factor authentication, etc.).
- IdP Issues a Token: Once authenticated, the IdP generates a session token or assertion (e.g., SAML, JWT, OAuth).
- Token is Used for Access: The user is redirected back to the original application (SP) with the authentication token, granting access.
- User Can Access Other Applications: Other connected applications recognize the SSO session and don’t require re-authentication.
SSO Protocols & Standards
SAML (Security Assertion Markup Language)
- XML-based protocol used in enterprise environments (e.g., Okta, Microsoft AD FS).
- Common in corporate intranets and cloud apps.
OAuth 2.0 + OpenID Connect (OIDC)
- OAuth 2.0 handles authorization & OpenID Connect adds authentication.
- Used for web & mobile apps (Google, Facebook, Microsoft Login).
Kerberos
Used in Windows Active Directory for secure authentication within corporate networks.
Pros & Cons of SSO
Benefits
- Improved User Experience - No need to log in multiple times.
- Stronger Security - Reduces password fatigue and reliance on weak passwords.
- Centralized Authentication - Easier to manage user access from one place.
- Reduces IT Costs - Fewer password reset requests.
Challenges & Risks
- Single Point of Failure - If the IdP goes down, users may be locked out.
- Security Risks - A compromised SSO account can grant access to multiple services.
- Implementation Complexity - Integrating different systems can be challenging.