The <channles/> configuration element is a complex attribute that is currently not allowed to be set via a property. We could enable this by adding a setter in the goals that use this parameter. The string value could be a URL or a GAV. As noted in a chat we could match the pattern ^(file|http|https)://.* and assume a URL. If not we use the groupId:artifactId:version (GAV) pattern to create the ChannelConfiguration.

<channels>
    <channel>
        <manifest>
            <groupId>org.wildfly.channels</groupId>
            <artifactId>wildfly-30.0</artifactId>
        </manifest>
    </channel>
</channels>

<channels>
    <channel>
        <manifest>
            <url>https://example.wildfly.org/channel/wildfly-30</url>
        </manifest>
    </channel>
</channels>

Note we should add an example and update the documentation for the channels property as well.