Overview
OAuth and SAML both let one system vouch for a user to another, but they solve different problems: OAuth is an authorization framework built to grant apps limited access to APIs, while SAML is an XML-based standard built for enterprise single sign-on. Picking the wrong one means using a token-delegation protocol for an identity-federation problem, or vice versa.
Comparison Diagram
Comparison Table
| Aspect | OAuth | SAML |
|---|---|---|
| Primary purpose | Authorization - grants an app limited, scoped access to resources | Authentication - proves a user’s identity for single sign-on |
| Assertion/token format | JSON, most commonly a JWT access token | XML, a digitally signed SAML assertion |
| Flow initiation | Client app redirects the user to an authorization server to request consent | Service provider redirects the user to an identity provider to authenticate |
| Credential delivery | Access token returned via redirect or back-channel to the client | Signed assertion POSTed back to the service provider’s endpoint |
| Transport mechanism | REST/HTTP calls carrying a bearer token in the Authorization header | HTTP redirect and POST bindings, historically also SOAP |
| Session establishment | Client presents the token on each API call to prove access rights | Service provider validates the assertion once and creates a local session |
| Lifetime and renewal | Short-lived access tokens paired with long-lived refresh tokens | Assertions tied to the SSO session with no built-in refresh mechanism |
| Typical ecosystem | Mobile apps, SPAs, and third-party API integrations (Google, GitHub) | Enterprise SSO into web apps via IdPs like Okta, ADFS, or Azure AD |
Key Differences
- OAuth is fundamentally an authorization framework, not an identity protocol, though OpenID Connect layers authentication on top of it.
- SAML assertions are XML-based and signed, while OAuth tokens are typically JSON, often as a JWT.
- SAML is built around browser redirects and POST bindings for SSO, while OAuth is built around bearer tokens for API calls.
- OAuth supports refresh tokens for renewing access; SAML assertions have no native renewal and rely on re-authentication.
When to Use Each
OAuth
- Third-Party API Access: OAuth lets a client app call a resource server’s API with a scoped, revocable access token instead of sharing credentials.
- Mobile & SPA Login: OAuth’s token-based model fits public clients that can’t securely store long-lived session state the way server-rendered apps can.
- Delegated Resource Access: OAuth is designed for scenarios where a user grants one app limited permission to act on their data held by another service.
SAML
- Enterprise Single Sign-On: SAML is the entrenched standard for letting employees authenticate once with a corporate IdP and access many internal web apps.
- Legacy Web App Integration: Many older enterprise SaaS platforms only support SAML-based SSO, not OAuth or OIDC, for federated login.
- Compliance-Driven Identity Federation: SAML’s signed XML assertions and mature audit trail fit regulated environments that require strict identity federation guarantees.