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{}),
	}
}
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{}),
	}
}
// 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