Security Assertion Markup Language (SAML) is an XML-based open standard used for exchanging authentication and authorization data between different security domains. SAML is most commonly used in Single Sign-On (SSO) scenarios, allowing users to access multiple applications or services without the need to log in repeatedly. It has become a critical technology for enabling secure identity management across web-based applications, particularly in enterprise environments and cloud services.

What Are Identity Providers (IdP) and Service Providers (SP)?

In the context of SAML, there are two primary roles:

  1. Identity Provider (IdP): The Identity Provider is responsible for authenticating the user. It validates the user’s credentials and generates an authentication assertion (SAML Assertion) that contains the user’s identity information. IdPs can be internal enterprise systems or third-party identity services like Google or Facebook.

  2. Service Provider (SP): The Service Provider is the entity that receives the authentication information (SAML Assertion) from the IdP and grants access to the requested service. The SP uses the identity information provided by the IdP to determine the user’s access rights and permissions.

SAML 2.0 Protocol Workflow Diagram

The typical workflow for SAML 2.0 involves several steps:

  1. User Accesses the Service Provider: The user attempts to access a service provided by an SP.
  2. SP Detects No Valid Session: The SP recognizes that there is no valid session or authentication token and redirects the user to the IdP for authentication.
  3. User Authenticates with IdP: The user enters their credentials (e.g., username and password) on the IdP’s authentication page.
  4. IdP Validates Credentials: The IdP verifies the user’s credentials and generates a SAML assertion containing the authenticated user’s identity information.
  5. IdP Sends Assertion to SP: The IdP sends the SAML assertion back to the SP, typically via an HTTP redirect.
  6. SP Validates the Assertion: The SP verifies the SAML assertion’s authenticity and ensures that it hasn’t been tampered with.
  7. Access Granted: If the assertion is valid, the SP grants the user access to the requested service.

This flow ensures that user authentication is handled centrally by the IdP, while the SP trusts the IdP’s assertions for granting access.

Comparing SAML with OAuth2 and OIDC

While SAML, OAuth2, and OpenID Connect (OIDC) are all widely used for authentication and authorization, they are designed for slightly different purposes and operate in distinct ways.

  • SAML: Primarily focused on authentication and often used in enterprise environments. SAML is heavily XML-based and works well for Single Sign-On (SSO) scenarios where multiple applications or services need to authenticate users seamlessly without repeated logins.

  • OAuth2: OAuth 2.0 is a framework designed for authorization. It allows third-party applications to gain limited access to a user’s resources without needing to handle the user’s credentials. OAuth2 is more flexible than SAML and is often used in modern applications, especially mobile apps and APIs. OAuth2 works based on tokens and doesn’t inherently support authentication, which is why it is often paired with OpenID Connect.

  • OpenID Connect (OIDC): OIDC is an authentication layer built on top of OAuth2. It adds a standardized method for performing authentication by using JSON Web Tokens (JWT) and includes user information. OIDC is modern and user-friendly, making it a common choice for web and mobile applications.

While SAML is more suited for enterprise and legacy applications, OAuth2 and OIDC are more aligned with modern application architectures, especially those involving APIs and mobile applications.

Conclusion

SAML plays a critical role in enabling secure authentication, especially in enterprise environments where Single Sign-On (SSO) is essential. By understanding the roles of Identity Providers (IdP) and Service Providers (SP) and how SAML 2.0 operates, organizations can implement a robust identity management system that streamlines user access and enhances security. However, in modern application development, OAuth2 and OIDC are often preferred for their flexibility and support for modern web and mobile applications.