User Management for Jira provides a workflow post function that lets you run most of the actions available in Scheduled User actions or Bulk User actions on a workflow transition.
The User Management Action post function can run an action, for example "Deactivate" on a user selected from one of the transitioning issues fields, for example the assignee or any custom field that contains the user's user key.
Because the User Management actions can have effects that are only accessible to administrators, by default the post function is restricted from being used and access must be explicitly granted to individual projects. Restrictions can be configured from the Project Restrictions screen. If the post function is added to a transition in a project that has not been granted access, then that transition will always fail and no action will be taken.