code: @SneakyThrows
      public RSAPrivateKey loadPrivateKey(String privateKeyLocation) {
          Resource keyRes = resourceLoader.getResource(privateKeyLocation);
          byte[] keyBytes = StreamUtils.copyToByteArray(keyRes.getInputStream());
          PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(keyBytes);
          KeyFactory keyFactory = KeyFactory.getInstance("RSA");
          RSAPrivateKey privateKey = (RSAPrivateKey) keyFactory.generatePrivate(privateKeySpec);
          return privateKey;
      }
docs: Given a resource location it loads a DER RSA private Key.
  
  @param privateKeyLocation
  @return