OAuth 2.0 PKCE Authorization Code Flow secures mobile and native app authentication by adding a cryptographic code verifier to prevent authorization code interception attacks. The flow spans four phases: PKCE setup where the app generates a code challenge, user authentication via system browser redirect, token exchange at the authorization server, and finally resource API access using the obtained access token. This pattern eliminates the need for client secrets in public clients, making it the recommended approach for mobile, desktop, and single-page applications. Fork this diagram on Diagrams.so to customize it for your OAuth provider, add custom scopes, or integrate with your documentation. PKCE (Proof Key for Code Exchange) is now mandatory for public clients under OAuth 2.0 security best practices.