Single Sign-On (SSO) - One Login for All Apps

About 2 min read

Single sign-on (SSO: Single Sign-On) is a mechanism that allows access to multiple services and applications with a single authentication. Users no longer need to enter a separate password for each service, greatly improving convenience. It is widely adopted in corporate internal systems and cloud services. According to a 2024 Okta survey, employees use an average of more than 80 SaaS apps per person, and the importance of SSO continues to grow.

The Difference Between SSO and OAuth

SSO and OAuth are related technologies, but they solve different problems. SSO provides the authentication convenience of "logging in to multiple services with a single authentication." OAuth provides the authorization security of "delegating permissions to an app without handing over your password." On the implementation side, SSO is realized through protocols such as SAML 2.0 and OpenID Connect (OIDC). OIDC adds an authentication layer on top of OAuth 2.0, integrating OAuth's authorization functionality with SSO's authentication functionality. For enterprise SSO, SAML is mainstream, while OIDC is mainstream for consumer-facing social login.

How SSO Works

In SSO, a central authentication server (IdP: Identity Provider) centrally manages user authentication. When a user completes authentication at the IdP, an authentication token is issued, and each linked service verifies this token to grant access. Representative IdPs include Okta, Azure AD, and Google Workspace.SSO and identity management books on Amazon offer a deeper understanding.

Real-World Use Cases

"After integrating our SSO platform with Okta, employees no longer needed an average of 12 passwords each. Password reset requests to the IT help desk were also reduced by 70%."

The SSO Flow

Risks and Countermeasures in Practice

SSO is convenient, but it carries the risk of becoming a "single point of failure." If SSO credentials are leaked, all linked services are affected. To mitigate this risk, set an especially strong random password for the SSO account and always enable multi-factor authentication. A common pitfall in practice is to think that "password management is unnecessary" just because SSO has been introduced. Services that do not support SSO still exist, and they require their own strong individual passwords. It is also important to consider the risk of being unable to log in to any service when the SSO provider has an outage, and to secure an emergency bypass method in advance.enterprise security books (Amazon) are also a helpful reference.