code: function hmacSign (input, algorithm, secret) {
    return crypto.createHmac(algorithm, secret).update(input).digest('base64')
  }
docs: private utils function
   
  hmac sign
  @param  {String} input     hamc sign input
  @param  {String} algorithm hamc sign algorithm
  @param  {String} secret    hamc sign secret
  @return {String}           hamc signature