code: func CryptoPublicKey(publicKey []byte) (crypto.PublicKey, error) {
  	// reuse the same RSA keys for SSH and TLS keys
  	pubKey, _, _, _, err := ssh.ParseAuthorizedKey(publicKey)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	cryptoPubKey, ok := pubKey.(ssh.CryptoPublicKey)
  	if !ok {
  		return nil, trace.BadParameter("expected ssh.CryptoPublicKey, got %T", pubKey)
  	}
  	return cryptoPubKey.CryptoPublicKey(), nil
  }
docs: // CryptoPublicKey extracts public key from RSA public key in authorized_keys format