Overview
SAML (Security Assertion Markup Language) and OpenID Connect (OIDC) are the two dominant protocols for implementing Single Sign-On across applications. SAML is an XML-based standard that has been the backbone of enterprise SSO since the mid-2000s, while OpenID Connect is a modern identity layer built on top of OAuth 2.0 that uses lightweight JSON Web Tokens. Both solve the same fundamental problem — allowing users to authenticate once and access multiple services — but they differ significantly in architecture, token formats, and ideal use cases.Choosing between SAML and OIDC depends on your environment and requirements. Enterprise organizations with legacy systems and established identity providers like Active Directory Federation Services often rely on SAML, while teams building modern web and mobile applications increasingly prefer OIDC for its simplicity and developer experience. Understanding the trade-offs between these protocols is essential for architects designing authentication systems that must serve both legacy and modern applications.
Quick Comparison
| Feature | SAML | OpenID Connect |
|---|---|---|
| Token Format | XML assertions | JSON Web Tokens (JWT) |
| Transport | HTTP Redirect, POST, Artifact | HTTP REST/JSON |
| Year Introduced | 2005 (SAML 2.0) | 2014 |
| Built On | Standalone XML standard | OAuth 2.0 |
| Mobile Support | Poor — XML parsing overhead | Excellent — native JSON support |
| Complexity | High — verbose XML schemas | Lower — simpler token structure |
| Enterprise Adoption | Very high | Growing rapidly |
| Discovery | Metadata XML document | Well-known discovery endpoint |
SAML Explained
SAML is an open standard that defines an XML-based framework for exchanging authentication and authorization data between an identity provider (IdP) and a service provider (SP). When a user attempts to access a service, the SP redirects them to the IdP, which authenticates the user and returns a signed XML assertion containing identity claims. The SP validates the assertion's digital signature and grants access based on the embedded attributes.
SAML 2.0 supports multiple bindings (HTTP Redirect, HTTP POST, and Artifact) and profiles that define specific use cases like Web Browser SSO and Single Logout. Its rich attribute statement capabilities allow IdPs to pass detailed user information such as roles, group memberships, and organizational data. This flexibility has made SAML the standard for enterprise federated identity scenarios, particularly in sectors like healthcare, government, and finance where established IdPs already support the protocol.
OpenID Connect Explained
OpenID Connect is an identity layer built on top of OAuth 2.0 that adds user authentication to the authorization framework. While OAuth 2.0 handles delegated authorization (granting applications access to resources), OIDC extends it with an ID Token — a JWT containing claims about the authenticated user. This clean separation allows developers to implement both authentication and authorization using a single, coherent protocol stack.
OIDC defines multiple flows suited to different application types: the Authorization Code flow for server-side web applications, the Authorization Code flow with PKCE for single-page and mobile applications, and a UserInfo endpoint for retrieving additional profile data. Its use of JSON rather than XML makes payloads smaller and easier to parse, which is particularly beneficial for mobile and IoT environments. A standardized discovery mechanism (the .well-known/openid-configuration endpoint) simplifies integration by allowing clients to automatically discover provider capabilities.
Key Differences
Token Format and Size
SAML assertions are XML documents that include digital signatures, conditions, and attribute statements, often resulting in payloads of several kilobytes. OpenID Connect ID Tokens are compact JWTs — Base64-encoded JSON objects that are typically under one kilobyte. This size difference has practical implications: SAML assertions can exceed URL length limits when using HTTP Redirect binding, while JWTs travel comfortably in HTTP headers and are trivially parsed by any programming language with a JSON library.
Protocol Architecture
SAML is a standalone protocol with its own extensive specification covering bindings, profiles, and metadata schemas. OpenID Connect is layered on top of OAuth 2.0, inheriting its authorization endpoints, token endpoints, and well-understood grant types. This means teams already familiar with OAuth 2.0 can adopt OIDC with relatively low learning overhead, while SAML requires understanding a separate and more complex specification ecosystem.
Mobile and Modern Application Support
SAML was designed in an era of server-rendered web applications and relies heavily on browser redirects with XML payloads. This makes it cumbersome to implement in mobile apps, single-page applications, and API-driven architectures. OpenID Connect was built with these modern architectures in mind, offering native JSON payloads, purpose-built flows for mobile clients (Authorization Code with PKCE), and seamless integration with REST APIs.
When to Use SAML
- Enterprise SSO with existing infrastructure — If your organization already uses SAML-based identity providers such as ADFS, PingFederate, or Shibboleth, and your service providers support SAML, maintaining SAML avoids unnecessary migration risk and leverages established trust relationships.
- Regulatory and compliance requirements — Certain industries and government frameworks explicitly reference SAML for federated identity interoperability, making it the path of least resistance for compliance.
- Rich attribute exchange — When you need to pass complex, multi-valued attributes about users (such as detailed role hierarchies or organizational unit data) in a standardized format, SAML's attribute statements provide a well-defined mechanism.
When to Use OpenID Connect
- Modern web and mobile applications — OIDC's JSON-based tokens and purpose-built flows make it the natural choice for single-page applications, native mobile apps, and microservices architectures.
- Developer experience and speed — OIDC's simpler specification, extensive library support across languages, and standardized discovery endpoints significantly reduce integration time compared to SAML.
- API-first architectures — When your authentication system must integrate with OAuth 2.0-protected APIs, OIDC provides a unified approach to both identity verification and API authorization using compatible token formats.
Can You Use Both?
Yes, and many organizations do. A common pattern is to deploy an identity provider that supports both SAML and OIDC simultaneously. Legacy enterprise applications connect via SAML while newer applications use OIDC — the IdP handles protocol translation behind the scenes. Solutions like Keycloak, Okta, and Azure AD natively support both protocols, allowing organizations to maintain backward compatibility while adopting modern standards for new development. Over time, many organizations are gradually migrating SAML integrations to OIDC, but a forced cutover is rarely necessary.
Frequently Asked Questions
What is the difference between SAML and OIDC?
SAML is an XML-based protocol designed for enterprise SSO that exchanges authentication data through verbose XML assertions. OpenID Connect is a modern identity layer built on OAuth 2.0 that uses compact JSON Web Tokens. While both enable single sign-on, OIDC is simpler to implement, better suited for mobile and modern web applications, and provides a more developer-friendly experience.
Should I use SAML or OIDC?
If you are building new applications, especially for web or mobile, OIDC is the recommended choice due to its simplicity, modern architecture, and broad library support. If you are integrating with existing enterprise systems that already use SAML, it may be pragmatic to continue with SAML for those integrations while adopting OIDC for new projects. Many identity providers support both, so the decision need not be all-or-nothing.
Is SAML more secure than OIDC?
Neither protocol is inherently more secure than the other — both can be implemented securely or insecurely. SAML uses XML digital signatures and encryption, while OIDC relies on JWTs with digital signatures and TLS for transport security. The security of either approach depends on correct implementation: validating signatures, enforcing token expiration, preventing replay attacks, and following each protocol's security best practices. OIDC benefits from being a newer specification that incorporates lessons learned from earlier protocols.