code: func (c *Cluster) GetUnlockKey() (string, error) {
  	var resp *swarmapi.GetUnlockKeyResponse
  	if err := c.lockedManagerAction(func(ctx context.Context, state nodeState) error {
  		client := swarmapi.NewCAClient(state.grpcConn)
  
  		r, err := client.GetUnlockKey(ctx, &swarmapi.GetUnlockKeyRequest{})
  		if err != nil {
  			return err
  		}
  		resp = r
  		return nil
  	}); err != nil {
  		return "", err
  	}
  	if len(resp.UnlockKey) == 0 {
  		// no key
  		return "", nil
  	}
  	return encryption.HumanReadableKey(resp.UnlockKey), nil
  }
docs: // GetUnlockKey returns the unlock key for the swarm.