public IUserGroup RegisterGroup(IList <IUser> users, string groupName, string password)
        {
            IRegistrantGroup group = this.CreateGroup(users, groupName, password);

            group.Register();
            return(group);
        }
        public IUserGroup ChangeGroupPassword(IUserGroup group, string password, string newPassword)
        {
            IRegistrantGroup registrantGroup = this.CreateGroup(group, password);

            registrantGroup.ChangePassword(newPassword);
            return(registrantGroup);
        }
        public IUserGroup RegisterGroup(IUserGroup group, string password)
        {
            IRegistrantGroup registrantGroup = this.CreateGroup(group, password);

            registrantGroup.Register();
            return(group);
        }