otp

type OTP struct {
	// Issuer represents the service provider. It is you! e.g. your service,
	// your application, your organisation so on.
	Issuer string
	// Account represents the service user. It is the user! e.g. username, email
	// address so on.
	Account string
	// Secret is an arbitrary key value encoded in Base32 and belongs to the
	// service user.
	Secret string
	// Window is used for time (TOTP) and counter (HOTP) synchronization. Given
	// that the possible time and counter drifts between client and server, this
	// parameter helps overcome such issue. TOTP uses backward and forward time
	// window whereas HOTP uses look-ahead counter window that depends on the
	// Counter parameter.
	// Resynchronisation is an official recommended practise, however the
	// lower the better.
	// 0 = not recommended as synchronization is disabled
	//   TOTP: current time
	//   HOTP: current counter
	// 1 = recommended option
	//   TOTP: previous - current - next
	//   HOTP: current counter - next counter
	// 2 = being overcautious
	//   TOTP: previous,previous - current - next,next
	//   HOTP: current counter - next counter - next counter
	// * = Higher numbers may cause denial-of-service attacks.
	// https://datatracker.ietf.org/doc/html/rfc6238#page-7
	// https://datatracker.ietf.org/doc/html/rfc4226#page-11
	Window int
	// Counter is required for HOTP only and used for provisioning the code. Set
	// it to 0 if you with to use TOTP. Start from 1 for HOTP then fetch and use
	// the one in the persistent storage. The server counter is incremented only
	// after a successful code verification, however the counter on the code is
	// incremented every time a new code is requested by the user which causes
	// counters being out of sync. For that reason, time-synchronization should
	// be enabled.
	// https://datatracker.ietf.org/doc/html/rfc4226#page-11
	Counter int
}