private static ByteString encodeSecretBigInteger(SecretBigInteger i, SecretKeyAccess access) {
    return encodeBigInteger(i.getBigInteger(access));
  }
Encodes a BigInteger using a big-endian encoding.
java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1ProtoSerialization.java