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, 26 insertions, 0 deletions

diff --git a/spec/services/audit_event_service_spec.rb b/spec/services/audit_event_service_spec.rb
new file mode 100644
index 00000000000..32fd98e6ef9
--- /dev/null
+++ b/spec/services/audit_event_service_spec.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe AuditEventService do
+  let(:project) { create(:project) }
+  let(:user) { create(:user) }
+  let(:project_member) { create(:project_member, user: user) }
+  let(:service) { described_class.new(user, project, { action: :destroy }) }
+  let(:logger) { instance_double(Gitlab::AuditJsonLogger) }
+
+  describe '#security_event' do
+    before do
+      expect(service).to receive(:file_logger).and_return(logger)
+    end
+
+    it 'creates an event and logs to a file' do
+      expect(logger).to receive(:info).with(author_id: user.id,
+                                            entity_id: project.id,
+                                            entity_type: "Project",
+                                            action: :destroy)
+
+      expect { service.security_event }.to change(SecurityEvent, :count).by(1)
+    end
+  end
+end