We always need to know which user is currently logged in. jBPM recognizes users with their actor ID and group actor ID. We specify the current actor IDs with the built-in Seam component, actor:

@In Actor actor;

public String login() {
  ...
  actor.setId( user.getUserName() );
  actor.getGroupActorIds().addAll( user.getGroupNames() );
  ...
}