The engine-rest/web.xml:"Http Basic Authentication" filter configuration doesn't contain the <async-supported>true</async-supported> property. This causes the /external-task/fetchAndLock endpoint to fail with a Failed processing arguments of org.jboss.resteasy.spi.metadata.ResourceMethod error.

The property needs to be added in all of the appropriate application server web.xml files and the documentation updated to reflect the changes.