SAML vs OAuth: Which Protocol Should You Choose?

Introduction

When implementing Single Sign-On (SSO), one of the first decisions you'll face is choosing between SAML and OAuth/OpenID Connect. Both protocols can achieve similar outcomes, but they have different strengths and are suited to different use cases. This article breaks down everything you need to know to make the right choice.

A Brief History

SAML (Security Assertion Markup Language)

SAML was developed in 2001 by OASIS, with SAML 2.0 released in 2005. It was designed specifically for enterprise web-based SSO and has been the industry standard for nearly two decades.

OAuth 2.0 & OpenID Connect

OAuth 1.0 emerged in 2007 as a way to authorize third-party access to resources (think "Login with Facebook"). OAuth 2.0 came in 2012, and OpenID Connect (OIDC) was built on top of OAuth 2.0 in 2014 to add identity layer capabilities.

How They Work

SAML Flow

User attempts to access a Service Provider (SP)

SP redirects to Identity Provider (IdP)

User authenticates with IdP

IdP generates SAML assertion (XML)

Browser posts assertion to SP

SP validates assertion and grants access

OAuth 2.0 + OIDC Flow

User attempts to access an application

Application redirects to Authorization Server

User authenticates

Authorization Server issues tokens (ID token, access token)

Application validates tokens and grants access

Key Differences

Data Format

| Aspect | SAML | OAuth/OIDC |

|--------|------|------------|

| Format | XML | JSON |

| Token Type | Assertion | JWT |

| Size | Larger (verbose XML) | Smaller (compact JSON) |

Use Cases

| Scenario | Better Choice |

|----------|---------------|

| Enterprise web SSO | SAML |

| Mobile applications | OAuth/OIDC |

| API authentication | OAuth/OIDC |

| Legacy enterprise systems | SAML |

| Modern SaaS applications | Either (OIDC preferred) |

| B2B customer portals | SAML |

Complexity

SAML: More complex initial setup, but well-documented enterprise patterns
OAuth/OIDC: Simpler to implement, but more flexibility can mean more decisions

When to Choose SAML

Choose SAML when:

Your identity provider primarily supports SAML

- Many enterprise IdPs like Okta, Azure AD, and OneLogin have better SAML support

You're integrating with enterprise customers

- B2B customers often expect SAML as it's the enterprise standard

You need rich attribute mapping

- SAML has more standardized attribute definitions

Compliance requirements specify SAML

- Some industries mandate SAML for certain use cases

You're dealing with legacy systems

- Older enterprise applications typically only support SAML

When to Choose OAuth/OIDC

Choose OAuth/OIDC when:

Building mobile or single-page applications

- OAuth was designed with these use cases in mind

You need API authorization

- OAuth's token-based approach is ideal for APIs

You want simpler implementation

- JSON is easier to work with than XML

Building consumer-facing applications

- Social logins (Google, Facebook) use OAuth

You need fine-grained authorization scopes

- OAuth's scope mechanism provides flexible permissions

Can You Support Both?

Absolutely! Many modern applications support both SAML and OIDC. This is often the best approach because:

Enterprise customers can use their preferred SAML-based IdPs
Smaller customers can use Google or other OIDC providers
Future flexibility as the industry evolves

SecurePie supports both protocols, allowing you to offer customers their preferred authentication method without any additional development work.

Implementation Considerations

Security Considerations

SAML Security:

Validate XML signatures carefully
Watch for XML injection attacks
Ensure proper certificate management

OAuth/OIDC Security:

Use PKCE for public clients
Validate tokens properly
Store tokens securely

Testing Your Implementation

Regardless of protocol choice:

Test with multiple identity providers

Verify attribute/claim mapping

Test session timeout handling

Validate error handling for edge cases

Perform security testing (signature validation, token expiry, etc.)

The Verdict

There's no universally "better" protocol—the right choice depends on your specific needs:

Enterprise B2B focus? → Start with SAML
Consumer apps or APIs? → Start with OAuth/OIDC
Want maximum flexibility? → Support both

At SecurePie, we've made this decision easy by supporting both protocols out of the box. Whether your customers use Okta with SAML or Google with OIDC, they get the same seamless SSO experience.

Next Steps

Ready to implement SSO for your Shopify store? Check out our integration guides: