code: func (d TLSCertKeyStore) GetKeyPair() (*rsa.PrivateKey, []byte, error) {
  	pk, ok := d.PrivateKey.(*rsa.PrivateKey)
  
  	if !ok {
  		return nil, nil, ErrNonRSAKey
  	}
  
  	if len(d.Certificate) < 1 {
  		return nil, nil, ErrMissingCertificates
  	}
  
  	crt := d.Certificate[0]
  
  	return pk, crt, nil
  }
docs: //GetKeyPair implements X509KeyStore using the underlying tls.Certificate