code: func sigHandler(nonce []byte, seedFile string) ([]byte, error) {
  	kp, err := nkeyPairFromSeedFile(seedFile)
  	if err != nil {
  		return nil, err
  	}
  	// Wipe our key on exit.
  	defer kp.Wipe()
  
  	sig, _ := kp.Sign(nonce)
  	return sig, nil
  }
docs: // Sign authentication challenges from the server.
  // Do not keep private seed in memory.