Having studied both SAML and OAuth, students often ask: 'Why do we need both?' The answer lies in the difference between *Authorization* (OAuth), *Authentication* (OIDC), and *Enterprise Identity* (SAML).
SAML is designed for the corporate environment. It excels at 'Single Sign-On' for web applications where the user and the application are both managed by a central corporate directory (like Active Directory).
Use SAML when you are building for a Fortune 500 company that requires a strict XML-based trust relationship and a corporate portal.
| Protocol | Primary Goal | Format | Typical User |
|---|---|---|---|
| SAML 2.0 | SSO / Enterprise Auth | XML | Employee $ o$ Corporate App |
| OAuth 2.0 | Delegated Authorization | JSON | App $ o$ API |
| OIDC | User Authentication | JSON (JWT) | Consumer $ o$ Website |
The key difference is that SAML is a complete package: it handles authentication, identity, and attributes in one signed XML document. OAuth only provides a token; it doesn't tell you *who* the user is, only *what* they can do.
💡 OIDC is a thin layer on top of OAuth 2.0. It adds an 'ID Token' (JWT) to the flow, finally giving OAuth the ability to provide identity (Authentication) in addition to access (Authorization).
// OIDC ID Token (The 'Who are you' part)
{
"iss": "https://accounts.google.com",
"sub": "123456789",
"email": "user@gmail.com",
"exp": 1600000000
}OIDC is the modern replacement for SAML in consumer apps. It is easier for developers to implement (JSON vs XML) and works perfectly on mobile devices via APIs.
Avoid using SAML for mobile apps. The XML parsing and browser-heavy redirects make for a poor mobile experience.
Never use OAuth 2.0 alone for authentication. Without OIDC (the ID token), you are performing 'Pseudo-Authentication,' which is a critical security flaw.
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