Security for web sites is a wide-ranging topic. It includes server security, network security, user authentication, data integrity, and cryptography to name a few. It is also true that one cannot neglect one of these aspects and focus on the others. We might have the most secure application ever, but it will still be vulnerable unless the server it's running on is also very secure.
In this chapter, we will cover the basics of each of these aspects of security. It will not be a full discussion of every vulnerability or every pitfall we need to avoid, but it will enable us to understand the aspects of security we need to look at when developing a web application.