One of the fundamental ways to secure a resource is to make sure that the caller is who they claim to be. This process of checking credentials and making sure that they are genuine is called authentication.
The following diagram shows the fundamental process Spring Security uses to address this core security requirement. The figure is generic and can be used to explain all the various authentication methods that the framework supports:
As detailed in Chapter 1, Overview of Spring 5 and Spring Security 5 (in the Working of Spring Security section), Spring Security has a series of servlet filters (a filter chain). When a request reaches the server, it is intercepted by this series of filters (Step 1 in the preceding diagram).
In the reactive world (with the new Spring WebFlux web application framework), filters are ...
