how to make variables declared within requiredproperties elements within required property element inside archetype-metadata.xml to be accessed from archetype post groovy script while writing custom archetype

Sample archetype-metadata.xml :

<requiredProperties>
<requiredProperty key="proxy-name">
    <defaultValue>${proxy.name}</defaultValue>
</requiredProperty>
<requiredProperty key="proxy-desc">
    <defaultValue>${proxy.description}</defaultValue>
</requiredProperty>

I want to fletch the value mentioned of proxy-name mentioned within archetype-metadata.xml and do certain specific options depending of the value of proxy-name variable with archetype post execution groovy script.