Starting from 2.7.x series, Apache CXF provides an additional asynch http client implementation: http://cxf.apache.org/docs/asynchronous-client-http-transport.html
The new transport is built on top of Apache HTTP Components HttpAsyncClient (http://hc.apache.org/httpcomponents-asyncclient-dev/index.html) and is automatically enabled (currently for asynch calls only) whenever the cxf-rt-transports-http-hc component is available. That is currently excluded from the dependency tree and not installed on the JBoss AS / WildFly as the HttpAsyncClient it transitively depends on is still at Beta level.