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[[core-eventNotification]]
=== Event Notification

You can set up event notifications in two ways. The sections that follow describe each approach in more detail.

* Register an event listener, ignoring events that do not interest you. Spring allows only partial event subscription; you use generics to register the class of events that interest you, and you are notified of that class and all subclasses.
* Register one or more callback closures in `grails-app/conf/application.groovy` that take advantage of the plugin's `grails.plugin.springsecurity.SecurityEventListener`. The listener does the filtering for you.

==== AuthenticationEventPublisher

Spring Security publishes events using an {apidocs}org/springframework/security/authentication/AuthenticationEventPublisher.html[AuthenticationEventPublisher] which in turn fire events using the {apidocs_spring}org/springframework/context/ApplicationEventPublisher.html[ApplicationEventPublisher]. By default no events are fired since the `AuthenticationEventPublisher` instance registered is a `grails.plugin.springsecurity.authentication.NullAuthenticationEventPublisher`. But you can enable event publishing by setting `grails.plugin.springsecurity.useSecurityEventListener = true` in `grails-app/conf/application.groovy`.

You can use the `useSecurityEventListener` setting to temporarily disable and enable the callbacks, or enable them per-environment.

==== UsernameNotFoundException

Most authentication exceptions trigger an event with a similar name as described in this table:

.Exceptions and associated events
[cols="50,50"]
|====================
| *Exception* | *Event*

|`AccountExpiredException`
|`AuthenticationFailureExpiredEvent`

|`AuthenticationServiceException`
|`AuthenticationFailureServiceExceptionEvent`

|`LockedException`
|`AuthenticationFailureLockedEvent`

|`CredentialsExpiredException`
|`AuthenticationFailureCredentialsExpiredEvent`

|`DisabledException`
|`AuthenticationFailureDisabledEvent`

|`BadCredentialsException`
|`AuthenticationFailureBadCredentialsEvent`

|`UsernameNotFoundException`
|`AuthenticationFailureBadCredentialsEvent`

|`ProviderNotFoundException`
|`AuthenticationFailureProviderNotFoundEvent`
|====================

This holds for all exceptions except `UsernameNotFoundException` which triggers an `AuthenticationFailureBadCredentialsEvent` just like a `BadCredentialsException`. This is a good idea since it doesn't expose extra information - there's no differentiation between a bad password and a missing user. In addition, by default a missing user will trigger a `BadCredentialsException` for the same reasons. You can configure Spring Security to re-throw the original `UsernameNotFoundException` instead of converting it to a `BadCredentialsException` by setting `grails.plugin.springsecurity.dao.hideUserNotFoundExceptions = false` in `grails-app/conf/application.groovy`.

Fortunately all subclasses of {apidocs}org/springframework/security/authentication/event/AbstractAuthenticationFailureEvent.html[AbstractAuthenticationFailureEvent] have a `getException()` method that gives you access to the exception that triggered the event, so you can use that to differentiate between a bad password and a missing user (if `hideUserNotFoundExceptions=false`).
