If you need to debug the request headers send to Wildfly application server you can configure a Request-Dumper. There for change the standalone.xml file and add a filter-ref and filter configuration into the subsystem section of undertow. See the following example:
...
<subsystem xmlns="urn:jboss:domain:undertow:2.0">
....
<server name="default-server">
...
<host name="default-host" alias="localhost">
.....
<filter-ref name="request-dumper"/>
</host>
</server>
....
<filters>
.....
<filter name="request-dumper" class-name="io.undertow.server.handlers.RequestDumpingHandler" module="io.undertow.core" />
</filters
This will print out all the request information send by a browser.