OAuth2 vs OIDC: Explained So Simply Anyone Can Understand

Read this first: OAuth2 Explained Clearly
See real-world integration: OAuth2 in SAP CPI and Informatica CAI

OAuth2 vs OIDC: Explained So Simply Anyone Can Understand

Most people confuse OAuth2 and OIDC.

They sound similar.
They are used together.
But they solve different problems.

Let’s make this very simple.

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🎯 The 1-Line Difference

• OAuth2 → What can the app do?
• OIDC → Who are you?

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🧠 Simple Story (Easy to Imagine)

🟢 OAuth2

You give a food delivery app permission to:

• see your address
• place orders

👉 The app can do things for you

🔵 OIDC

You log into a website and it knows:

• your name
• your email

👉 The app knows who you are

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📊 Visual Difference

flowchart LR
    A[OAuth2] --> B[Access to APIs]
    C[OIDC] --> D[User Identity]

    B --> E[Read data / Write data]
    D --> F[Name / Email / Profile]

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🔑 Tokens (Keep it Simple)

OAuth2 gives:

• Access Token → used to call APIs

OIDC gives:

• ID Token → used to identify the user
• (also uses access tokens for APIs)

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📦 Real Example (Google Login)

👉 “Continue with Google”

sequenceDiagram
    participant User
    participant App
    participant Google

    User->>Google: Login & consent
    Google->>App: ID Token (who user is)
    Google->>App: Access Token (what app can access)

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🧠 Easy Analogy

• OAuth2 = Permission Slip → “This app can access your stuff”
• OIDC = ID Card → “This is who you are”

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🎯 When to Use What

Use OAuth2 when:

• calling APIs
• accessing data
• integrations

Use OIDC when:

• login system
• user identity
• showing user profile

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⚠️ Common Mistake

Many apps assume OAuth2 tells them who the user is.

That’s wrong.

OAuth2 does NOT guarantee identity

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🔍 Where OAuth2 and OIDC Fit (Compared to Other Methods)

🔐 OAuth2

• Purpose: Authorization
• Use: API access

🪪 OIDC

• Purpose: Authentication (Identity)
• Built on: OAuth2
• Use: Login

🏢 LDAP

• Purpose: Directory + Authentication
• Use: Internal enterprise systems

🧾 SAML

• Purpose: Authentication (SSO)
• Use: Enterprise Single Sign-On

🧓 OAuth 1.0

• Purpose: Authorization (older)
• Status: Mostly replaced by OAuth2

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🧠 Simple Way to Remember

OAuth2 → Access
OIDC → Identity
LDAP → Internal users
SAML → Enterprise SSO
OAuth1 → Legacy

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🧭 Final Thought

Modern systems usually combine:

• OAuth2 → for access
• OIDC → for identity

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🔗 Related Reading

• OAuth2 Explained Clearly
• OAuth2 in SAP CPI and Informatica CAI