I was using the old config file.
Here's the new one explained here:
https://www.ovirt.org/documentation/administration_guide/
Example 21. Example authentication mapping configuration file
ovirt.engine.extension.name = example-http-mapping
ovirt.engine.extension.bindings.method = jbossmodule
ovirt.engine.extension.binding.jbossmodule.module = org.ovirt.engine.extension.aaa.misc
ovirt.engine.extension.binding.jbossmodule.class =
org.ovirt.engine.extension.aaa.misc.mapping.MappingExtension
ovirt.engine.extension.provides = org.ovirt.engine.api.extensions.aaa.Mapping
config.mapAuthRecord.type = regex
config.mapAuthRecord.regex.mustMatch = true
config.mapAuthRecord.regex.pattern =
^(?<user>.*?)((\\\\(?<at>@)(?<suffix>.*?)@.*)|(?<realm>@.*))$
config.mapAuthRecord.regex.replacement = ${user}${at}${suffix}