client, err := whmcs.NewClient(urlToWhmcs, username, password, dangerMode)
if err != nil {
	return err
}

login, err := client.Authentication.ValidateLogin(&whmcs.ValidateLoginRequest{
	Email:    whmcs.String("[email protected]"),
	Password: whmcs.String("password"),
})
if err != nil {
	return err
}