SAML vs OAuth vs OpenID Connect: Authentication Protocols Explained

Last updated October 2026

SAML, OAuth 2.0, and OpenID Connect are three distinct protocols that handle identity and access in web applications: SAML (Security Assertion Markup Language) provides enterprise single sign-on using XML assertions, OAuth 2.0 handles delegated authorisation (granting apps access to your data without sharing your password), and OpenID Connect adds an authentication layer on top of OAuth 2.0 to verify user identity. Understanding when to use each protocol is essential for developers building web applications, SaaS platforms, and enterprise software—choosing the wrong one leads to security vulnerabilities or unnecessary complexity.

What Problem Does Each Protocol Solve?

The three protocols address different aspects of identity and access:

• Authentication (AuthN): “Who are you?” — verifying a user’s identity. Solved by SAML and OpenID Connect.
• Authorisation (AuthZ): “What are you allowed to do?” — granting access to specific resources. Solved by OAuth 2.0.
• Single Sign-On (SSO): “Log in once, access many applications.” — enterprise users log into their corporate identity provider and access all connected applications. Solved by SAML and OpenID Connect.

The common confusion: OAuth 2.0 is not an authentication protocol. It does not tell your application who the user is—it provides a token that grants access to an API. OpenID Connect was created to add the authentication layer that OAuth lacks. SAML handles both authentication and attribute exchange but in a different (XML-based) format.

How Does SAML Work?

SAML is the oldest protocol (v2.0 released 2005) and remains the standard for enterprise SSO. The flow involves three parties:

1. User: The person trying to access an application.
2. Service Provider (SP): Your application (e.g., your SaaS product).
3. Identity Provider (IdP): The system that authenticates users (e.g., Okta, Azure AD, Google Workspace, OneLogin).

The SP-initiated flow (most common):

1. User tries to access your application.
2. Your application generates a SAML AuthnRequest (XML document) and redirects the user’s browser to the IdP.
3. The IdP authenticates the user (if not already logged in).
4. The IdP creates a SAML Assertion (XML document containing user identity and attributes), signs it with a digital certificate, and sends it to your application via the user’s browser (HTTP POST).
5. Your application validates the assertion’s signature, extracts user information, and creates a local session.

When to use SAML: Enterprise customers require it. If your SaaS product sells to Indian enterprises (banks, government, large corporates), they will ask for SAML SSO integration with their identity provider (typically Azure AD, Okta, or ADFS). SAML is also necessary for government systems and regulated industries where it is a compliance requirement.

When not to use SAML: Mobile applications (SAML is browser-based and XML-heavy), consumer-facing applications (too complex for social login), and new projects without enterprise requirements (OpenID Connect is simpler).

How Does OAuth 2.0 Work?

OAuth 2.0 handles delegated authorisation—allowing an application to access a user’s resources on another service without the user sharing their password. Example: your marketing tool needs access to a user’s Google Analytics data. OAuth 2.0 enables this.

Key parties:

• Resource Owner: The user who owns the data.
• Client: Your application that wants to access the data.
• Authorisation Server: The system that authenticates the user and issues tokens (e.g., Google’s OAuth server).
• Resource Server: The API that holds the user’s data (e.g., Google Analytics API).

The Authorization Code flow (recommended for web apps):

1. Your application redirects the user to the Authorisation Server with the requested scopes (permissions).
2. User logs in and grants your application the requested permissions.
3. Authorisation Server redirects back to your application with an authorisation code.
4. Your application exchanges the code for an access token (server-to-server, code never exposed to the browser).
5. Your application uses the access token to call the Resource Server’s API.

When to use OAuth 2.0: When your application needs to access another service’s API on behalf of the user—Google APIs, Facebook Graph API, GitHub API, Razorpay API, any third-party API that supports OAuth. Also used for machine-to-machine API access via the Client Credentials flow.

When not to use OAuth 2.0 alone: For user authentication. OAuth gives you an access token but does not reliably tell you who the user is. The access token is for API access, not identity verification. Use OpenID Connect for authentication.

How Does OpenID Connect (OIDC) Work?

OpenID Connect is an identity layer built on top of OAuth 2.0. It adds a standardised way to verify user identity and retrieve user profile information. Think of it as “OAuth 2.0 + authentication.”

OIDC adds to OAuth 2.0:

• ID Token: A JWT (JSON Web Token) containing the authenticated user’s identity information (subject ID, email, name, authentication time, etc.). This is the authentication proof that OAuth 2.0 lacks.
• UserInfo endpoint: A standard API endpoint that returns the user’s profile information.
• Standard scopes: openid (required), profile (name, picture), email, address, phone.
• Discovery: A .well-known/openid-configuration endpoint that advertises the provider’s capabilities, endpoints, and supported features.

The flow is identical to OAuth 2.0 Authorization Code flow, with the addition of the openid scope and the ID Token in the response.

When to use OpenID Connect: “Login with Google,” “Login with GitHub,” “Login with Microsoft”—any social or enterprise login in a modern web or mobile application. OIDC is the recommended protocol for new authentication implementations. Providers: Google, Microsoft, Apple, GitHub, Okta, Auth0, Keycloak.

SAML vs OAuth 2.0 vs OpenID Connect: Direct Comparison

• Purpose: SAML = Authentication + SSO; OAuth = Authorisation; OIDC = Authentication + SSO (on top of OAuth)
• Format: SAML = XML; OAuth/OIDC = JSON + JWT
• Transport: SAML = Browser redirects + HTTP POST; OAuth/OIDC = Browser redirects + API calls
• Mobile support: SAML = poor; OAuth/OIDC = excellent
• Complexity: SAML = high (XML parsing, certificate management); OIDC = moderate; OAuth = moderate
• Enterprise adoption: SAML = very high (legacy); OIDC = growing rapidly
• Best for: SAML = enterprise SSO; OAuth = API access delegation; OIDC = modern authentication

What Should Indian SaaS Developers Implement?

For an Indian SaaS product targeting both SMBs and enterprises:

1. Start with OpenID Connect for all authentication: “Login with Google,” “Login with Microsoft,” email/password (via Auth0, Clerk, or Firebase Auth which use OIDC internally).
2. Add OAuth 2.0 for any third-party API integrations your product needs (Google Workspace, Slack, HubSpot, etc.).
3. Add SAML when enterprise customers request it. Most Indian enterprises with 500+ employees have Azure AD or Okta and will require SAML or OIDC SSO as a procurement condition.

Use an authentication service (Auth0 from ₹1,700/month, Clerk, Firebase Auth free tier, or self-hosted Keycloak at ₹0 software cost) rather than building authentication from scratch. These services handle SAML, OAuth, and OIDC implementation, token management, session handling, and security updates.

Frequently Asked Questions

Can OIDC replace SAML for enterprise SSO?

Technically yes—OIDC can provide the same SSO functionality as SAML with simpler implementation. However, many enterprise identity providers and legacy applications only support SAML. In practice, you need to support both SAML and OIDC if selling to Indian enterprises. Large banks, government departments, and IT companies often have SAML-only identity infrastructure.

Is OAuth 2.0 secure?

OAuth 2.0 is a framework, not a specific implementation—its security depends on correct implementation. Common vulnerabilities: using the Implicit flow (deprecated, use Authorization Code with PKCE instead), not validating redirect URIs, not using state parameters (CSRF protection), storing tokens insecurely, and not implementing token refresh properly. Follow OAuth 2.0 Security Best Current Practice (RFC 9700) for secure implementation.

What is PKCE and why is it important?

PKCE (Proof Key for Code Exchange) is an extension to the OAuth 2.0 Authorization Code flow that prevents authorisation code interception attacks. It is mandatory for mobile apps and single-page applications, and recommended for all OAuth/OIDC implementations. The client generates a random code_verifier, sends a hashed code_challenge with the authorisation request, and provides the original code_verifier when exchanging the code for tokens. The server verifies they match.

How do you implement SSO for a multi-tenant Indian SaaS application?

Each tenant (customer organisation) configures their own identity provider (IdP). Store per-tenant IdP configuration: SAML metadata URL or OIDC discovery URL, client ID/secret, attribute mappings. When a user logs in, determine their tenant (from email domain or subdomain), redirect to that tenant’s IdP, and process the response with tenant-specific configuration. Services like Auth0 Organizations and WorkOS provide this multi-tenant SSO as a managed service.

What does the authentication landscape look like beyond these three protocols?

Emerging standards include Passkeys (FIDO2/WebAuthn) for passwordless authentication, Verifiable Credentials for decentralised identity, and Token Exchange (RFC 8693) for microservice-to-microservice authentication. For Indian developers, the immediate priority is solid OIDC implementation. Passkeys are gaining adoption (Google, Apple, Microsoft all support them) and may replace passwords for consumer authentication within 3-5 years.