Missing info, how to configure handler just for a deployment.
There are several options:

1. using jboss-web.xml
2. using META-INF/services + undertow-handlers.conf

You can find some info about the options in this specific comment on different JIRA: https://issues.jboss.org/browse/JBEAP-3893?focusedCommentId=13182967&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13182967.

There should be also noted that you can either use one of already implemented handlers or create your own.