Fixup servlet/authentication/architecture/index.adoc

docs/modules/ROOT/pages/servlet/authentication/architecture/index.adoc

@@ -3,7 +3,19 @@
 :figures: images/servlet/authentication/architecture
 :icondir: images/icons
 
-This discussion expands on <<servlet-architecture>> to discuss the Servlet Authentication architecture.
+This discussion expands on <<servlet-architecture>> to describe the main architectural components of Spring Security's used in Servlet authentication.
+If you need concrete flows that explain how these pieces fit together, look at the <<servlet-authentication-mechanisms,Authentication Mechanism>> specific sections.
+
+* <<servlet-authentication-securitycontextholder>> - The `SecurityContextHolder` is where Spring Security stores the details of who is <<authentication,authenticated>>.
+* <<servlet-authentication-securitycontext>> - is obtained from the `SecurityContextHolder` and contains the `Authentication` of the currently authenticated user.
+* <<servlet-authentication-authentication>> - Can be the input to `AuthenticationManager` to provide the credentials a user has provided to authenticate or the current user from the `SecurityContext`.
+* <<servlet-authentication-granted-authority>> - An authority that is granted to the principal on the `Authentication` (i.e. roles, scopes, etc.)
+* <<servlet-authentication-authenticationmanager>> -  the API that defines how Spring Security's Filters perform  <<authentication,authentication>>.
+* <<servlet-authentication-providermanager>> -  the most common implementation of `AuthenticationManager`.
+* <<servlet-authentication-authenticationprovider>> - used by `ProviderManager` to perform a specific type of authentication.
+* <<servlet-authentication-authenticationentrypoint>> - used for requesting credentials from a client (i.e. redirecting to a log in page, sending a `WWW-Authenticate` response, etc.)
+* <<servlet-authentication-abstractprocessingfilter>> - a base `Filter` used for authentication.
+This also gives a good idea of the high level flow of authentication and how pieces work together.
 
 [[servlet-authentication-securitycontextholder]]
 == SecurityContextHolder