According to the definition of the "org.wildfly.undertow.http-invoker.host" capability, it provides a PathHandler service[1], but the installed service[2] exposes the HttpInvokerHostService instance itself[3].

[1] https://github.com/jbossas/jboss-eap7/blob/7.x/undertow/src/main/java/org/wildfly/extension/undertow/HttpInvokerDefinition.java#L56
[2] https://github.com/jbossas/jboss-eap7/blob/7.x/undertow/src/main/java/org/wildfly/extension/undertow/HttpInvokerDefinition.java#L119
[3] https://github.com/jbossas/jboss-eap7/blob/7.x/undertow/src/main/java/org/wildfly/extension/undertow/HttpInvokerHostService.java