https://github.com/undertow-io/undertow/commit/2a7d9934c41aa023eda4b8b6eafb08f4991ec3b5 made ServletSessionConfig and SessionCookieConfig binary-incompatible vs the Undertow Core 2.4.0.Alpha1 used in WildFly Preview. Unfortuntately, the subsystem integration code (i.e. UndertowDeploymentInfoService, AffinitySessionConfigWrapper, HttpInvokerHostService) compiles against that class, so when it compiles against the 2.3 version it fails at runtime when using the 2.4 version.

I'll see if we can use reflection to deal with this.