Add support for JSON logging for audit events

This will add audit_json.log that writes one line per audit event. For
example:

{
       "severity":"INFO",
       "time":"2018-10-17T17:38:22.523Z",
       "author_id":3,
       "entity_id":2,
       "entity_type":"Project",
       "change":"visibility",
       "from":"Private",
       "to":"Public",
       "author_name":"John Doe4",
       "target_id":2,
       "target_type":"Project",
       "target_details":"namespace2/project2"
}

1 files changed, 22 insertions, 4 deletions

diff --git a/app/services/audit_event_service.rb b/app/services/audit_event_service.rb
index 4c5e22bdd7e..201048aaba5 100644
--- a/app/services/audit_event_service.rb
+++ b/app/services/audit_event_service.rb
@@ -17,11 +17,29 @@ class AuditEventService
   end
 
   def security_event
-    SecurityEvent.create(
+    log_security_event_to_file
+    log_security_event_to_database
+  end
+
+  private
+
+  def base_payload
+    {
       author_id: @author.id,
       entity_id: @entity.id,
-      entity_type: @entity.class.name,
-      details: @details
-    )
+      entity_type: @entity.class.name
+    }
+  end
+
+  def file_logger
+    @file_logger ||= Gitlab::AuditJsonLogger.build
+  end
+
+  def log_security_event_to_file
+    file_logger.info(base_payload.merge(@details))
+  end
+
+  def log_security_event_to_database
+    SecurityEvent.create(base_payload.merge(details: @details))
   end
 end