docs: public static PrivateKey loadPrivateKey(File privateKeyFile) throws InvalidKeySpecException, IOException {
          if ( StringUtils.lowerCase(privateKeyFile.getAbsolutePath()).endsWith(".pem") ) {
              InputStream is = new FileInputStream(privateKeyFile);
              try {
                  return PEM.readPrivateKey(is);
              } finally {
                  try {is.close();} catch(IOException ignore) {}
              }
          } else if ( StringUtils.lowerCase(privateKeyFile.getAbsolutePath()).endsWith(".der") ) {
              InputStream is = new FileInputStream(privateKeyFile);
              try {
                  return RSA.privateKeyFromPKCS8(IOUtils.toByteArray(is));
              } finally {
                  try {is.close();} catch(IOException ignore) {}
              }
          } else {
              throw new AmazonClientException("Unsupported file type for private key");
          }
      }