Generally a provisioner in the framework (built-in or custom) will have a first class provisioner implementation. i.e. you see it in the drop down, it has specific configuration and validation etc.
However, if you want to implement a custom generic provisioner and not write all the classes and configs to make that happen, you can use the generic provisioner. Just implement a DAO class and register it in the provisioner. All the configs specific to this provisioner should live elsewhere in the configuration, not with the provisioner configuration or external system.
This is an example of using this
