OAuth 2.0 vs SAML: Choosing the Right Protocol

We get asked about OAuth versus SAML constantly, usually framed as a simple “which one should we use?” The answer is almost never straightforward because these protocols solve overlapping but distinct problems, and most enterprise environments end up using both.

Let’s cut through the confusion.

They’re Not Really Competitors

SAML (Security Assertion Markup Language) is an authentication and authorization protocol designed in 2005 for enterprise single sign-on. It’s XML-based, built for browser-based flows, and deeply embedded in enterprise identity infrastructure.

OAuth 2.0 is an authorization framework from 2012, designed to let applications access resources on behalf of users. It’s typically JSON-based, works well with mobile and API scenarios, and underpins most modern “Login with Google/Facebook/GitHub” flows.

OpenID Connect (OIDC) is an identity layer built on top of OAuth 2.0, adding authentication capabilities. When people compare “OAuth vs SAML” for authentication, they usually mean “OIDC vs SAML.”

The confusion comes from the fact that both can enable single sign-on, but they approach the problem differently and excel in different contexts.

SAML: The Enterprise Workhorse

SAML dominates enterprise SSO for good reason. It was designed specifically for the problem of authenticating users across organizational boundaries—exactly what enterprises need when connecting employees to SaaS applications.

How SAML works (simplified):

1. User tries to access an application (the Service Provider)
2. Application redirects to the Identity Provider (Okta, Azure AD, etc.)
3. User authenticates with the IdP
4. IdP sends a signed XML assertion back to the application
5. Application validates the assertion and logs the user in

The XML assertion contains claims about the user—name, email, group memberships, whatever attributes the SP needs. The IdP signs this assertion cryptographically, so the SP can trust it without directly communicating with the IdP.

Where SAML shines:

• Mature enterprise SaaS integrations (Salesforce, Workday, ServiceNow all speak SAML fluently)
• IT-controlled authentication flows where browser redirects are acceptable
• Organizations with existing SAML infrastructure and expertise
• Regulatory environments where SAML’s track record provides comfort
• Federation scenarios connecting multiple organizations

Where SAML struggles:

• Mobile applications (those XML payloads and browser redirects are painful on mobile)
• Single-page applications and modern JavaScript frontends
• API authorization (SAML wasn’t designed for machine-to-machine scenarios)
• Lightweight integrations where SAML’s complexity isn’t justified

OAuth 2.0 and OIDC: The Modern Approach

OAuth 2.0 was built for a different era—one of mobile apps, APIs, and third-party integrations. It’s fundamentally about authorization (letting an app access your data) rather than authentication (proving who you are), but OIDC adds the identity layer that makes it useful for SSO.

How OAuth 2.0/OIDC works (simplified):

1. User clicks “Login with [Provider]”
2. Application redirects to the authorization server
3. User authenticates and grants consent
4. Provider redirects back with an authorization code
5. Application exchanges the code for tokens (access token, ID token, refresh token)
6. Application uses the ID token for identity, access token for API calls

The token-based approach fits modern architectures. Access tokens are short-lived and scoped. Refresh tokens enable long sessions without constant re-authentication. The whole system was designed with APIs in mind.

Where OAuth 2.0/OIDC shines:

• Mobile applications (tokens work naturally in mobile contexts)
• Single-page applications and modern frontends
• API authorization and microservices
• Social login integrations
• Consumer-facing applications
• Scenarios requiring granular consent and scopes

Where OAuth 2.0/OIDC struggles:

• Legacy enterprise applications expecting SAML
• Organizations with heavy SAML investments and no appetite for change
• Scenarios where the IdP doesn’t support OIDC (yes, some still don’t)

The Real-World Decision

Most organizations don’t get to choose one or the other—they inherit SAML for enterprise applications and need OAuth/OIDC for modern development. The question becomes which to use for new integrations and how to manage the coexistence.

Use SAML when:

• Integrating with enterprise SaaS that expects it
• Your IdP is SAML-centric and OIDC support is weak
• Compliance requirements specifically call for SAML
• The integration is browser-based with no mobile/API requirements

Use OAuth 2.0/OIDC when:

• Building mobile applications
• Building SPAs or modern web applications
• API authentication is required
• You need granular authorization scopes
• Social login is part of the user experience
• Your IdP has strong OIDC support (most modern ones do)

Use both when:

• You’re an enterprise with legacy SAML applications AND new modern development
• You need to support both workforce and customer identity scenarios
• Different applications have different requirements

Identity Provider Capabilities

Your IdP choice often determines what’s practical. Modern identity platforms (Okta, Azure AD, Auth0) support both protocols well. Older or more limited platforms might push you toward one or the other.

Questions to ask:

• Does the IdP support OIDC natively, or only through awkward bridging?
• What’s the quality of SAML metadata and OIDC discovery endpoints?
• How are attributes/claims mapped in each protocol?
• What’s the operational experience for each protocol in your IdP?

If your IdP’s OIDC implementation is buggy or limited, SAML might be more reliable even for scenarios where OIDC would theoretically be better.

Security Considerations

Both protocols are secure when implemented correctly. The common vulnerabilities come from implementation mistakes, not protocol design.

SAML security concerns:

• XML signature wrapping attacks (mostly mitigated in modern libraries)
• Assertion replay if not properly validated
• Complex XML processing that’s historically been vulnerability-prone

OAuth 2.0/OIDC security concerns:

• Token leakage through improper storage or transmission
• Authorization code interception (mitigated by PKCE)
• Open redirect vulnerabilities
• Confused deputy problems with token validation

In practice, both protocols are battle-tested. Use well-maintained libraries, follow current best practices, and avoid implementing crypto yourself. The protocol choice matters less than implementation quality.

Migration Paths

Organizations often want to modernize from SAML to OIDC. This is possible but rarely urgent unless SAML is causing real problems.

Gradual migration approach:

1. Deploy an IdP that supports both protocols well
2. Implement OIDC for new applications
3. Migrate existing applications opportunistically (when they’re updated anyway)
4. Keep SAML for applications that would be expensive to change

There’s no need to rip out working SAML integrations. The protocols coexist fine, and many applications will never justify migration costs.

The Token vs Assertion Philosophy

One way to think about the difference: SAML is about assertions (the IdP asserts facts about the user to the SP), while OAuth is about tokens (the authorization server issues tokens that applications present to access resources).

Assertions are typically validated at login time. The SP trusts the assertion and creates a local session. The user’s identity is established, and that’s mostly the end of the IdP’s involvement.

Tokens are validated on every request. APIs check access tokens constantly. This model fits architectures where authorization decisions happen at the resource level, not just at login.

Neither model is superior—they reflect different assumptions about how authentication and authorization should work.

Implementation Complexity

SAML implementations tend to involve more upfront configuration (metadata exchange, attribute mapping, certificate management) but are relatively stable once working. The XML tooling is mature if unexciting.

OAuth 2.0/OIDC implementations can start simpler (especially with hosted IdPs) but may involve more ongoing complexity—token lifecycle management, scope design, refresh token strategies. The ecosystem is more fragmented, with more choices to make.

Development teams generally find OIDC more intuitive if they’re building from scratch. Operations teams managing enterprise SSO often find SAML more familiar.

What We Actually Recommend

For new projects without legacy constraints:

• Customer-facing applications: OAuth 2.0/OIDC. The mobile support alone makes this obvious.
• Internal web applications: OIDC if your IdP supports it well, SAML if that’s where your organization’s expertise lies.
• APIs and microservices: OAuth 2.0. SAML wasn’t designed for this.
• Enterprise SaaS integrations: Whatever the SaaS vendor prefers (usually SAML).

For existing environments:

• Don’t migrate working SAML integrations without a compelling reason.
• Use OIDC for new development to build that muscle.
• Ensure your IdP can bridge between protocols for applications that need it.

The goal isn’t protocol purity—it’s authentication that’s secure, maintainable, and appropriate for each use case.