public IActionResult SearchUserForInvitation([FromBody] SearchUserForInvitationRequest request)
        {
            var result = _userFacade.FindUsersForInvite(request.Username, request.GroupId, request.WantToTeach);
            var items  = new List <MinUserForInvitationItem>();

            result.ToList().ForEach(res => items.Add(
                                        new MinUserForInvitationItem(res.Invited, res.Username, res.IsTeacher, res.Id, res.AvatarLink)
                                        ));
            var response = new MinUserForInvitationResponse(items);

            return(Ok(response));
        }