It protects client-side code, server-side logic, sessions, data, interfaces, and supporting configuration against unauthorized access, unsafe interpretation of input, abuse of browser trust, and other application-layer failures. The scope includes design, implementation, deployment, testing, monitoring, and remediation — not only perimeter filtering.
Web applications cross several trust boundaries: browser to server, one origin to another, application to data store, service to service, and code to third-party content. Security depends on preserving those boundaries while applying authorization and business rules to every sensitive action.
Key points
Core controlsUse secure session handling, server-side authorization, context-appropriate input and output handling, protected transport, safe error behavior, least privilege, and controlled integration with dependencies.
Browser-aware designAccount for origins, cookies, framing, navigation, script execution, content loading, client-side storage, and the difference between browser-enforced policy and server-side trust decisions.
Verification and operationReview architecture and code, test authenticated roles and workflows, evaluate deployment configuration, monitor abuse and failures, and reassess after changes to the application or platform.
Important limitationA scanner or web application firewall can detect or block selected patterns, but neither can establish correct business logic, complete authorization, secure design, or adequate coverage of every application state.