Work Assignment in Lifecycles
If you want to assign a task in an Entity Modeling Lifecycle to a specific user, you can follow follwing procedure:
Create the Lifecycle
Create a lifecycle, e.g. like this:

Do not directly use tasks for user intreaction, but sub processes. In this case: Apply Retention Period.
Business process
Create a BPMN based business process:

In this example, you can see two tasks:
- In the response of the first task (web service call) the user name of the responsible user will be sent.
- The second task is an Entity Layout (user interface).
How to insert Entity Layouts in business processes
To insert an Entity Layout to a business process right click on a free space in the modeler and select Insert -> Entity Layout:

Select your layout.
Work assignment
Open the properties of the task Apply Retention Period and go to the tab Work Assignment

In this example, the user name is part of the output message of the previous task. Select Read from Message and open the XPath editor.
XPath expression
Provide following expression to get the full qualified user name:

The element Owner contains the user name.