Add explanation for DelegatingAuthenticationFailureHandler (#207)

docs/manual/src/docs/asciidoc/index.adoc

@@ -2772,7 +2772,7 @@ The login form simply contains `username` and `password` input fields, and posts
 
 [[form-login-flow-handling]]
 ==== Application Flow on Authentication Success and Failure
-The filter calls the configured `AuthenticationManager` to process each authentication request. The destination following a successful authentication or an authentication failure is controlled by the `AuthenticationSuccessHandler` and `AuthenticationFailureHandler` strategy interfaces, respectively. The filter has properties which allow you to set these so you can customize the behaviour completely  footnote:[In versions prior to 3.0, the application flow at this point had evolved to a stage was controlled by a mix of properties on this class and strategy plugins. The decision was made for 3.0 to refactor the code to make these two strategies entirely responsible.]. Some standard implementations are supplied such as `SimpleUrlAuthenticationSuccessHandler`, `SavedRequestAwareAuthenticationSuccessHandler`, `SimpleUrlAuthenticationFailureHandler` and `ExceptionMappingAuthenticationFailureHandler`. Have a look at the Javadoc for these classes and also for `AbstractAuthenticationProcessingFilter` to get an overview of how they work and the supported features.
+The filter calls the configured `AuthenticationManager` to process each authentication request. The destination following a successful authentication or an authentication failure is controlled by the `AuthenticationSuccessHandler` and `AuthenticationFailureHandler` strategy interfaces, respectively. The filter has properties which allow you to set these so you can customize the behaviour completely  footnote:[In versions prior to 3.0, the application flow at this point had evolved to a stage was controlled by a mix of properties on this class and strategy plugins. The decision was made for 3.0 to refactor the code to make these two strategies entirely responsible.]. Some standard implementations are supplied such as `SimpleUrlAuthenticationSuccessHandler`, `SavedRequestAwareAuthenticationSuccessHandler`, `SimpleUrlAuthenticationFailureHandler`, `ExceptionMappingAuthenticationFailureHandler` and `DelegatingAuthenticationFailureHandler`. Have a look at the Javadoc for these classes and also for `AbstractAuthenticationProcessingFilter` to get an overview of how they work and the supported features.
 
 If authentication is successful, the resulting `Authentication` object will be placed into the `SecurityContextHolder`. The configured `AuthenticationSuccessHandler` will then be called to either redirect or forward the user to the appropriate destination. By default a `SavedRequestAwareAuthenticationSuccessHandler` is used, which means that the user will be redirected to the original destination they requested before they were asked to login.