Your workflow must have the following defined as an Input Paramater.

[Properties]payload     = Custom Properties from vRA.

To access these

var machine = payload.get("machine") ;
 
// From the Machine Object, you get fetch the real Custom Properties:
 
var vCACVmProperties = machine.get("properties") ;
if (vCACVmProperties != null) 
{
	var array = new Array();
	for each (var key in vCACVmProperties.keys) 
        {
		array.push(key + " : " + vCACVmProperties.get(key));	
	}
	array.sort();
 
	for each (var line in array) 
        {
		System.log (line + "\n");
	}	
}

Your workflow must have the following defined as an Output Paramater, in addiontal the event must be run as blocking.

[Properties] virtualMachineDeleteProperties      = Contains list of properties to delete, value does not matter.
[Properties] virtualMachineAddOrUpdateProperties = Contains list of properties to create or update. **Value CANNOT be null! (vRA will Crash!)**
[string] virtualMachineEvent = "BuildFailure" or "BuildSuccess"

Note: Setting the virtualMachineEvent to "BuildFailure" will NOT result in the rest of the events not to be  triggered, this all depends witch event you are in. However "Cleanup" events will be triggered after "Success" events are triggered.
Note2: Setting the virtualMachineEvent to "BuildSucess" will say that the machine is "finished" (runs the same events later on as BuildFailure
Note3: These can only be used in Events that Support vCacProperties (See Tables)

If you set “BuildFailure” or “BuildSucess” in or after VMPSMasterWorkflow32.BuildingMachine Post event (After Template is cloned and VM is customized) MachineProvisioned and MachineActived events will stil trigger.

If you set “BuildFailure” in the VMPSMasterWorkflow32.Requested events. The machine will still be cloned. UNLESS you also set it in the VMPSMasterWorkflow32.BuildingMachine PRE event

If you set “BuildFailure” in the VMPSMasterWorkflow32.BuildingMachine PRE event, the template will not be cloned.