Good access control systems (and its management) are key to an application's security.
Trust boundaries are the gatekeepers for data in your applications.
Using the DREAD threat modeling framework you can get a better view of the risk of your application.
Knowing the exposed points of your application can help heighten your security and defenses.
Attack patterns provide a common language to refer to threat types and methods of attack.
Part of the "Core Concepts" series, examines the "Defence in Depth" thought pattern to secure your app.