WebSerivce subsystem has a user reported issue [1] which ws endpoint can't declare an undertow subsystem application security domain in jboss-web.xml. I had a quick look and it looks we need an injector to get undertow's ApplicationSecurityDomain and finally get the elytron security domain like what we handle ejb application security domain right now [2].
To make this work, I write some workaround code [3], and this may better explain what ws integration code expects to fix this issue. Darren and Stuart, can you please have a look and let me know your ideas and thoughts about this issue? 

[1]https://developer.jboss.org/message/977628
[2] https://github.com/wildfly/wildfly/blob/master/webservices/server-integration/src/main/java/org/jboss/as/webservices/service/EndpointService.java#L100
[3] https://github.com/jimma/wildfly/commit/d93b8ac89e388c54a10ce627780486143267e052

Thanks,
Jim