SAML vs OAuth/OIDC: A Comparison for Azure AD

Introduction

In the realm of identity and access management, particularly within the Azure Active Directory (Azure AD) ecosystem, understanding the differences between Security Assertion Markup Language (SAML) and the OAuth 2.0/OpenID Connect (OIDC) framework is crucial. Both protocols facilitate single sign-on (SSO) and secure access to applications, but they operate on different principles and are suited for different use cases. This article breaks down these differences, helping you make informed decisions for your organization.

What is SAML?

SAML is an XML-based open standard for exchanging authentication and authorization data between parties, an identity provider (IdP) and a service provider (SP). When a user tries to access a protected resource on an SP, the SP redirects the user's browser to the IdP. The IdP authenticates the user and then sends a SAML assertion (an XML document) back to the SP, confirming the user's identity and attributes. Azure AD can act as an IdP for SAML-based applications.

Key Characteristics of SAML:

Protocol Type: Token-based exchange, primarily for authentication.
Data Format: XML.
Use Cases: Traditionally used for web-based SSO, especially in enterprise environments where applications are often pre-integrated.
Flow: Involves redirects between the user's browser, the SP, and the IdP.
Focus: Strong focus on federated identity and single sign-on between different security domains.

What are OAuth 2.0 and OpenID Connect?

OAuth 2.0 is an authorization framework that allows users to grant third-party applications limited access to their resources on another service without exposing their credentials. OpenID Connect (OIDC) is a simple identity layer built on top of the OAuth 2.0 protocol. OIDC allows client applications to verify the identity of the end-user based on the authentication performed by an authorization server and to obtain basic profile information about the end-user. Azure AD is a robust provider of both OAuth 2.0 and OIDC.

Key Characteristics of OAuth 2.0/OIDC:

Protocol Type: Authorization framework (OAuth 2.0) and identity layer (OIDC), often using JSON Web Tokens (JWT).
Data Format: JSON (often via JWTs).
Use Cases: Modern applications, mobile apps, APIs, and scenarios requiring delegated authorization.
Flow: More flexible flows (e.g., Authorization Code Grant, Implicit Grant) can involve redirects or direct API calls.
Focus: Delegation of access, user consent, and obtaining identity information in a modern, API-friendly manner.

SAML vs. OAuth/OIDC: A Direct Comparison

Let's compare these protocols head-to-head in the context of Azure AD integration.

Feature	SAML (with Azure AD)	OAuth 2.0 / OIDC (with Azure AD)
Primary Function	Authentication and Authorization (Federation)	Authorization (OAuth 2.0) & Authentication (OIDC)
Data Format	XML	JSON (often JWT)
Flow Complexity	Can be complex due to XML parsing and redirect handling.	Generally considered more streamlined for modern web/mobile.
Typical Use Cases	Enterprise web applications, SaaS integrations, federating with existing identity systems.	Mobile applications, single-page applications (SPAs), API security, modern web apps, social logins.
Tokens	SAML Assertions (XML)	Access Tokens, ID Tokens (JWT)
User Identity Information	Attributes within the SAML assertion.	Claims within the ID Token (OIDC) or accessible via UserInfo endpoint.
Azure AD Integration	Azure AD acts as a SAML 2.0 Identity Provider.	Azure AD acts as an Authorization Server and OpenID Connect Provider.
Mobile App Support	Less common, often requires custom integration.	Excellent, designed with mobile and SPAs in mind.
API Security	Can secure APIs, but often less direct than OAuth.	Primary protocol for securing APIs via Bearer Tokens.

When to Use Which with Azure AD?

The choice between SAML and OAuth/OIDC often depends on the application's architecture and requirements:

Choose SAML when:

Integrating with legacy enterprise applications that already support SAML.
Your organization has a strong existing SAML-based federation strategy.
You need to assert user identity and attributes to a service provider across different security domains without exposing credentials.

Choose OAuth 2.0 / OIDC when:

Developing modern web applications, single-page applications (SPAs), or mobile applications.
You need to secure APIs and grant granular access permissions.
You want to enable delegated authorization or "login with Azure AD" features.
Interoperability with a wide range of modern services and platforms is a priority.

Important Note: Azure AD supports both SAML and OAuth/OIDC protocols for application integration. You can register an application in Azure AD and configure it to use either SAML-based SSO or OAuth/OIDC-based sign-in, depending on the application's requirements.

Conclusion

Both SAML and OAuth/OIDC are powerful standards for managing authentication and authorization with Azure AD. SAML excels in traditional enterprise federation scenarios, while OAuth 2.0 and OIDC are the go-to protocols for modern, API-driven applications and mobile experiences. By understanding their distinct strengths and characteristics, you can effectively leverage Azure AD to secure your applications and provide a seamless user experience.