code: func ParseSigningKeyStorePEM(keyPEM, certPEM string) (*SigningKeyStore, error) {
  	_, err := ParseCertificatePEM([]byte(certPEM))
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	key, err := ParsePrivateKeyPEM([]byte(keyPEM))
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	rsaKey, ok := key.(*rsa.PrivateKey)
  	if !ok {
  		return nil, trace.BadParameter("key of type %T is not supported, only RSA keys are supported for signatures", key)
  	}
  	certASN, _ := pem.Decode([]byte(certPEM))
  	if certASN == nil {
  		return nil, trace.BadParameter("expected PEM-encoded block")
  	}
  	return &SigningKeyStore{privateKey: rsaKey, cert: certASN.Bytes}, nil
  }
docs: // ParseSigningKeyStore parses signing key store from PEM encoded key pair