code: func (s *IdentityService) GetUser(user string) (services.User, error) {
  	if user == "" {
  		return nil, trace.BadParameter("missing user name")
  	}
  	item, err := s.Get(context.TODO(), backend.Key(webPrefix, usersPrefix, user, paramsPrefix))
  	if err != nil {
  		return nil, trace.NotFound("user %q is not found", user)
  	}
  	u, err := services.GetUserMarshaler().UnmarshalUser(
  		item.Value, services.WithResourceID(item.ID), services.WithExpires(item.Expires))
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return u, nil
  }
docs: // GetUser returns a user by name