SAML vs OAuth 2.0 vs OIDC: A Practical Deep Dive with Architecture & API Access Flows

🧠 Core Concepts

📌 High-level comparison of SAML vs OAuth 2.0 vs OIDC

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🔐 SAML (Security Assertion Markup Language)

• XML-based legacy protocol for Single Sign-On (SSO)

• Common in enterprise apps

• Provides a one-time SAML assertion during login

• Does not support modern API access directly

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🔓 OAuth 2.0

• Delegated access model (Authorization)

• Scopes define what can be accessed

• Access Token & Refresh Token issued

• Does not provide identity by itself

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🔗 OIDC (OpenID Connect)

• Identity layer on top of OAuth 2.0

• Adds ID Token to represent the user

• Supports web, mobile, and APIs

• Modern alternative to SAML

📌OAuth + OIDC flow

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🧾 Use Case: Cross-App API Access

Scenario

• You have App A (browser app) authenticated via SSO

• App A needs to access App B and App C APIs

• User should not re-login for App B/C data

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🎯 Implementation Options

✅ Option 1: SAML-Based (Legacy)

• App A authenticates via SAML SSO

• App B and C require separate API access

• No native token support → need OAuth bridge

• ❌ Not seamless for API access

✅ Option 2: OAuth 2.0 + OIDC (Recommended)

• App A uses OIDC to authenticate

• Access Token allows API calls to App B/C

• All via standard JWT tokens

• ✅ Seamless and secure

✅ Option 3: Hybrid Model

• Use SAML for login

• Issue OAuth tokens via token exchange

• Requires extra setup (like Azure AD or custom IdP logic)

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💡 What is an Identity Provider (IdP)?

A system that:

• Authenticates the user

• Issues tokens (SAML Assertion / ID Token / Access Token)

Popular IdPs:

• Azure AD

• Okta

• Auth0

• Google Identity

📌IdP role in auth ecosystem

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🔐 Azure Active Directory (Azure AD)

• Supports both SAML and OAuth/OIDC

• Central user and app management

• App registration enables:

  • Token issuance

  • Scopes and claims

  • SSO across applications

Example: App A calls App B API using token from Azure AD

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📊 Comparison Summary

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🔄 Token Flow with OIDC

1. App A → Redirect to IdP (Azure AD)

2. IdP authenticates → returns ID Token + Access Token

3. App A uses Access Token to call App B’s API

4. App B validates token and responds with data

📌 OIDC Token flow for browser + API

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✅ Recommendation

For modern apps needing login + API access:

• Use OIDC over OAuth 2.0

• Register all apps in a central IdP (like Azure AD)

• Use access tokens for cross-app API communication

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📝 Final Words

SAML has served enterprise SSO for years, but it falls short in a modern API-first world.

OAuth 2.0 + OIDC provides:

• Lightweight tokens

• Secure access control

• Seamless experience across apps and APIs

Migrate if possible, and embrace the token-driven future.

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📢 Feedback or Questions?

Drop a comment or message :

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