SSO vs SAML vs OAuth vs OIDC: Understanding Modern Authentication & Authorization

In today's digital world, seamless and secure access to applications is crucial. But with so many authentication and authorization protocols—SSO, SAML, OAuth, and OIDC—understanding their differences can be overwhelming.

🔹 SSO (Single Sign-On)
What it is: A system that allows users to log in once and access multiple applications without needing to re-enter credentials.
How it works: It centralizes authentication through an identity provider (IdP).
Example: Logging into Google and automatically getting access to Gmail, YouTube, and Google Drive.

🔹 SAML (Security Assertion Markup Language)
What it is: A standard for exchanging authentication and authorization data between an Identity Provider (IdP) and a Service Provider (SP).
How it works: Uses XML-based assertions to transmit user authentication info.
Use case: Enterprise SSO solutions (e.g., logging into multiple company applications with a single login).
Example: Logging into Salesforce using your company's credentials.

🔹 OAuth (Open Authorization)
What it is: A framework for authorization, allowing users to grant third-party apps limited access to their resources without exposing credentials.
How it works: Uses access tokens instead of passwords.
Use case: Allowing apps to act on behalf of users (e.g., read email, post on social media).
Example: "Login with Google/Facebook" for third-party apps.

🔹 OIDC (OpenID Connect)
What it is: An authentication layer built on top of OAuth 2.0.
How it works: Provides identity information (who the user is) in JSON Web Tokens (JWTs).
Use case: Logging users into an app while also verifying their identity.
Example: Using Google to log into a website while also retrieving user profile info.

How They Relate

SSO = Concept of logging in once to access multiple applications.
SAML= An authentication standard mostly used in enterprise SSO.
OAuth = An authorization framework, not focused on authentication.
OIDC = Extends OAuth 2.0 to include authentication.

Which One to Use?

SAML→ Best for enterprise SSO with internal business applications.
OAuth→ Best for granting third-party access to resources (e.g., APIs).
OIDC→ Best for modern authentication (e.g., mobile & web login with identity verification).
SSO→ A broader concept that can use SAML or OIDC.