OAuth Implementation Implement OAuth 2.0 and OpenID Connect for secure authentication. OAuth 2.0 Flows | Flow | Use Case | |------|----------| | Authorization Code | Web apps (most secure) | | Authorization Code + PKCE | SPAs, mobile apps | | Client Credentials | Service-to-service | | Refresh Token | Session renewal | Authorization Code Flow (Express) PKCE for Public Clients Security Requirements - Always use HTTPS - Validate redirect URIs strictly - Use PKCE for public clients - Store tokens in HttpOnly cookies - Implement token rotation - Use short-lived access tokens (15 min) Additional I…