🔍 Why This Matters
Whether you’re building a web app, mobile app, or integrating third-party services, OAuth 2.0 is the backbone of secure delegated access. But many developers treat it as a black box.
Let’s break it down, step-by-step, in a developer-friendly way, with no jargon.
🧠What Is OAuth 2.0?
OAuth 2.0 is not an authentication protocol (despite how it’s often used). It’s an authorization framework — it allows one system (like your app) to access resources from another system (like Google, GitHub, or your own API) without exposing the user’s credentials.
🧩 Core Concepts
| Term | Meaning |
|---|---|
| Resource Owner | The user who gives access (e.g., you) |
| Client | The app requesting access (e.g., your web/mobile app) |
| Authorization Server | The system that issues tokens (e.g., accounts.google.com) |
| Resource Server | The API the client wants to access (e.g., Google Drive, your API) |
| Access Token | A short-lived token to access protected resources |
| Refresh Token | A long-lived token to get new access tokens when old ones expire |
🛠️ Grant Types (OAuth Flows)
Let’s look at the most common types:
1. Authorization Code Flow (most secure, used by web apps)
Step 1: User logs into the auth provider (e.g., Google)
Step 2: They approve access
Step 3: Your app receives a code
Step 4: Your backend exchanges code for access token
Step 1: App authenticates directly with auth server using client_id and secret
Step 2: Receives access token
3. Implicit Flow (deprecated, insecure — avoid)
All token exchange happens in frontend JS (not recommended)
4. Password Grant (used when you trust the client — now discouraged)
User provides username/password directly to the app
🧪 Sample Token Response
{ "access_token": "abc123", "token_type": "Bearer", "expires_in": 3600, "refresh_token": "def456" }
You can now send this token in API requests:
GET /user/data HTTP/1.1 Authorization: Bearer abc123
⚠️ Common Mistakes
- Mixing OAuth with Login/Auth: Use OpenID Connect (OIDC) if you need identity.
- Storing tokens insecurely: Always encrypt refresh tokens and store access tokens safely.
- Not rotating tokens: Always build logic to refresh and revoke tokens securely.
🧠Final Thoughts
OAuth 2.0 powers login systems, file-sharing apps, fintech platforms, and more. As a developer, you don’t need to memorize the spec — just understand the flows and handle tokens securely.
Whenever you’re using APIs or integrating third-party auth, chances are OAuth is the key.
Further Reading: