## What is OAuth?
OAuth is a secure authorization protocol that lets users grant applications access to their data without sharing passwords. You see it when websites offer "Sign in with Google" or "Login with GitHub."
Instead of creating yet another account, you authorize the app to access specific information from your existing account elsewhere.
## The Problem OAuth Solves
**Old Way**: To let App A access your data from App B, you give App A your App B password. Terrible idea - App A could do anything with your account.
**OAuth Way**: You authorize App A to access only specific data (like email or profile) without ever sharing your password. You can revoke this access anytime.
## How OAuth Works
1. You click "Sign in with Google" on a website
2. Redirected to Google, who asks "Allow this app to access your email and profile?"
3. You approve
4. Google gives the app an access token (not your password)
5. App uses token to request your data from Google
6. You stay logged into Google separately; the app only has limited access
Your password never leaves Google. The app gets limited, revocable access.
## Real-World Examples
**Login**: Most websites now offer OAuth login (Google, Facebook, GitHub, Apple). Fewer passwords to remember, faster signup.
**Integrations**: Slack reading your Google Calendar, Trello syncing with GitHub, Spotify showing your Facebook friends. All powered by OAuth.
**Mobile Apps**: Apps accessing your contacts, photos, or location after you grant permission - that is OAuth under the hood.
## OAuth vs Passwords
**With Passwords**:
- App stores your password (security risk)
- App has full access to your account
- Cannot revoke access without changing password
- Password must be shared with every app
**With OAuth**:
- App never sees your password
- App gets only requested permissions
- Revoke access anytime from one place
- One authorization works for multiple apps
## Common OAuth Providers
**Google OAuth**: Access Gmail, Drive, Calendar, user profile.
**GitHub OAuth**: Access repositories, user info, manage repos.
**Facebook Login**: Access profile, friends list, email.
**Twitter OAuth**: Post tweets, read timeline, access profile.
## Developer Perspective
Implementing OAuth means you do not manage passwords. No password resets, no security vulnerabilities from weak passwords, no storing sensitive data.
Users trust established providers (Google, GitHub) more than new apps. Offering OAuth login increases signup rates.
## OAuth Versions
**OAuth 1.0**: Original version, complex, rarely used now.
**OAuth 2.0**: Current standard, simpler, more flexible. What most services use today.
**OpenID Connect**: Built on OAuth 2.0, adds identity layer. Provides user info along with authorization.
## Security Considerations
OAuth is secure when implemented correctly. Common mistakes:
- Not validating tokens properly
- Using insecure redirect URLs
- Exposing client secrets in frontend code
- Not using HTTPS (required for OAuth)
Most developers use libraries that handle OAuth correctly. Do not implement from scratch unless necessary.
## User Control
OAuth gives users control. From your Google account, you can see every app with access and revoke any of them instantly. The app stops working but your Google account stays secure.
This control makes OAuth privacy-friendly and user-centric.
## Why OAuth Matters
OAuth powers modern web integrations. Almost every "Connect with..." button uses OAuth. Understanding it is essential for building applications that integrate with other services or offer social login.
It transformed how applications share data securely, making the web more connected while keeping users safer.
