This chapter shows you how to use security in your Spring Boot applications to secure your web application. You learn everything from using basic security to using OAuth. Security has become a primary and important factor for desktop, web, and mobile applications in the last decade. But security is a little hard to implement because you need to think about everything—cross-site scripting, authorization, and authentication, secure sessions, identification, encryption, and a lot more. There is still a lot to do to implement simple security in your applications.