code: public static ApnsSigningKey loadFromPkcs8File(final File pkcs8File, final String teamId, final String keyId) throws IOException, NoSuchAlgorithmException, InvalidKeyException {
          try (final FileInputStream fileInputStream = new FileInputStream(pkcs8File)) {
              return ApnsSigningKey.loadFromInputStream(fileInputStream, teamId, keyId);
          }
      }
docs: Loads a signing key from the given PKCS#8 file.
  
  @param pkcs8File the file from which to load the key
  @param teamId the ten-character, Apple-issued identifier for the team to which the key belongs
  @param keyId the ten-character, Apple-issued identitifier for the key itself
  
  @return an APNs signing key with the given key ID and associated with the given team
  
  @throws IOException if a key could not be loaded from the given file for any reason
  @throws NoSuchAlgorithmException if the JVM does not support elliptic curve keys
  @throws InvalidKeyException if the loaded key is invalid for any reason