rack watch for user_id events

lib/datadog/appsec/contrib/rack/gateway/watcher.rb

@@ -21,6 +21,7 @@ def watch
                 watch_request(gateway)
                 watch_response(gateway)
                 watch_request_body(gateway)
+                watch_user_id(gateway)
               end
 
               def watch_request(gateway = Instrumentation.gateway)
@@ -152,8 +153,47 @@ def watch_request_body(gateway = Instrumentation.gateway)
                 end
               end
 
+              def watch_user_id(gateway = Instrumentation.gateway)
+                gateway.watch('identity.set_user', :appsec) do |stack, user|
+                  block = false
+                  event = nil
+                  waf_context = Datadog::AppSec::Processor.current_context
+
+                  AppSec::Reactive::Operation.new('identity.set_user') do |op|
+                    trace = active_trace
+                    span = active_span
 
-                [ret, res]
+                    Rack::Reactive::SetUser.subscribe(op, waf_context) do |result, _block|
+                      if result.status == :match
+                        # TODO: should this hash be an Event instance instead?
+                        event = {
+                          waf_result: result,
+                          trace: trace,
+                          span: span,
+                          user: user,
+                          actions: result.actions
+                        }
+
+                        span.set_tag('appsec.event', 'true') if span
+
+                        waf_context.events << event
+                      end
+                    end
+
+                    _result, block = Rack::Reactive::SetUser.publish(op, user)
+                  end
+
+                  next [nil, [[:block, event]]] if block
+
+                  ret, res = stack.call(request)
+
+                  if event
+                    res ||= []
+                    res << [:monitor, event]
+                  end
+
+                  [ret, res]
+                end
               end
 
               private