code: func New(accountSid, apiKey, apiSecret, identity string, ttl time.Duration) *AccessToken {
  	return &AccessToken{
  		accountSid: accountSid,
  		apiKey:     apiKey,
  		apiSecret:  []byte(apiSecret),
  		identity:   identity,
  		ttl:        ttl,
  		grants:     make(map[string]interface{}),
  	}
  }
docs: // New generates a new AccessToken with the specified properties. identity is
  // a unique ID for a particular user.
  //
  // To generate an apiKey and apiSecret follow this instructions:
  // https://www.twilio.com/docs/api/rest/access-tokens#jwt-format