docs: function digitalSignature(custom, request, epoch) {
      /**
       * Node Crypto Sign object that uses the given algorithm.
       *
       * @see {@link https://nodejs.org/api/crypto.html#crypto_class_sign}
       */
      const signer = crypto_1.createSign('RSA-SHA256');
      /**
       * Walmart API request string to be signed.
       */
      let stringToSign = custom.WMConsumer.ConsumerId + "\n" + request.RequestUrl + "\n"
          + request.RequestMethod.toUpperCase() + "\n" + epoch + "\n";
      /**
       * Updates the Sign content with the given data.
       * @see {@link https://nodejs.org/api/crypto.html#crypto_sign_update_data_inputencoding}
       */
      signer.update(stringToSign);
      /**
       * Private key wrapped in key header and footer.
       */
      let privateKey = "-----BEGIN PRIVATE KEY-----\n" + request.PrivateKey + "\n-----END PRIVATE KEY-----";
      return signer.sign(privateKey, 'base64');
  }