When a client app (e.g. a JavaEE application client) wants to perform a login to a WildFly 11 server, it has to either use a "wildfly-config.xml" file or add some code to setup security (see e.g. Client authentication with Elytron client for a code snippet).

To make this code compile, two jar files are required:
%WILDFLY11_HOME%\modules\system\layers\base\org\wildfly\security\elytron-private\main\wildfly-elytron-1.1.1.Final.jar
%WILDFLY11_HOME%\modules\system\layers\base\org\wildfly\common\main\wildfly-common-1.2.0.Final.jar

I think the runtime should add them by default.