+.new
+.cindex authentication "failure event"
+If an authenticator is run and does not succeed,
+an event (see &<<CHAPevents>>&) of type "auth:fail" is raised.
+While the event is being processed the variables
+&$sender_host_authenticated$& (with the authenticator name)
+and &$authenticated_fail_id$& (as set by the suthenticator &%server_set_id%& option)
+will be valid.
+See <<CHAPevents>> for details on events.
+.wen