diff --git a/testing/http_authentication.rst b/testing/http_authentication.rst
index ff1f0d49a90..c6abf4d6a8d 100644
--- a/testing/http_authentication.rst
+++ b/testing/http_authentication.rst
@@ -116,6 +116,8 @@ needs::
             // the firewall context defaults to the firewall name
             $firewallContext = 'secured_area';
 
+            // you may need to use a different token class depending on your application.
+            // for example, when using Guard authentication you must instantiate PostAuthenticationGuardToken
             $token = new UsernamePasswordToken('admin', null, $firewallContext, array('ROLE_ADMIN'));
             $session->set('_security_'.$firewallContext, serialize($token));
             $session->save();