code: func (nc *Conn) processAuthorizationViolation(err string) {
  	nc.mu.Lock()
  	nc.err = ErrAuthorization
  	if nc.Opts.AsyncErrorCB != nil {
  		nc.ach.push(func() { nc.Opts.AsyncErrorCB(nc, nil, ErrAuthorization) })
  	}
  	nc.mu.Unlock()
  }
docs: // processAuthorizationViolation is called when the server signals a user
  // authorization violation.