OAuth enables secure third-party access to user resources without sharing passwords, forming the backbone of modern API security and single sign-on.
Why it matters
- Eliminates password sharing between applications, reducing credential exposure.
- Enables granular permission scopes, limiting what third-party apps can access.
- Required for enterprise identity federation and API ecosystem security.
- Foundation for modern authentication protocols like OpenID Connect (OIDC).
How it works
- Authorization Grant: User approves access via consent screen.
- Access Token: Short-lived credential for API requests.
- Refresh Token: Long-lived token to obtain new access tokens.
- Scopes: Define specific permissions (read email, access calendar).
- Authorization Server: Issues tokens after validating user consent.
Common OAuth flows
- Authorization Code Flow: Most secure, used for web and mobile apps.
- Client Credentials Flow: Service-to-service authentication.
- Implicit Flow: Legacy browser-based flow (deprecated).
- PKCE Extension: Protects authorization code flow from interception.
Security considerations
- Always validate redirect URIs to prevent token theft.
- Use PKCE for mobile and single-page applications.
- Implement token rotation and expiration policies.
- Monitor for unusual authorization patterns or scope requests.
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