code: function rsaSign (input, algorithm, privateSecret) {
    try {
      // sign with rsa_private_key.pem
      return crypto.createSign(algorithm).update(input).sign(privateSecret, 'base64')
    } catch (e) {
      throw new Error(errorMap['003'].message)
    }
  }
docs: rsa sign
  @param  {String} input             rsa sign input
  @param  {String} algorithm         rsa sign algorithm
  @param  {String} privateSecret     rsa sign secret
  @return {String}                   rsa signature