public HttpResponseMessage PostLoginUser(UserModel model)
        {
            return this.PerformOperationAndHandleExceptions(() =>
            {
                var context = this.ContextFactory.Create();
                using (context)
                {
                    var usernameToLower = model.Username.ToLower();
                    var usersDbSet = context.Set<User>();
                    var entity = usersDbSet.SingleOrDefault(usr => usr.Username == usernameToLower && usr.AuthenticationCode == model.AuthCode);
                    if (entity == null)
                    {
                        var errResponse = this.Request.CreateErrorResponse(HttpStatusCode.BadRequest, "Invalid username or password");
                        throw new HttpResponseException(errResponse);
                    }

                    entity.SessionKey = this.GenerateSessionKey(entity.Id);

                    context.SaveChanges();
                    var responseModel = new LoginResponseModel()
                    {
                        Nickname = entity.Username,
                        SessionKey = entity.SessionKey
                    };

                    var response = this.Request.CreateResponse(HttpStatusCode.Accepted, responseModel);
                    return response;
                }
            });
        }
        public HttpResponseMessage PostRegisterUser(UserModel model)
        {
            return this.PerformOperationAndHandleExceptions(() =>
            {
                var usernameToLower = model.Username.ToLower();
                var context = this.ContextFactory.Create();
                using (context)
                {
                    var usersDbSet = context.Set<User>();
                    var entity = usersDbSet
                        .FirstOrDefault(usr => usr.Username == usernameToLower);
                    if (entity != null)
                    {
                        string responseMessage = "Username already taken";

                        HttpResponseMessage errResponse = this.Request.CreateErrorResponse(HttpStatusCode.Conflict, responseMessage);
                        throw new HttpResponseException(errResponse);
                    }
                    entity = new User()
                    {
                        Username = model.Username.ToLower(),
                        AuthenticationCode = model.AuthCode
                    };
                    usersDbSet.Add(entity);
                    context.SaveChanges();
                    return this.PostLoginUser(model);
                    //return response;
                }
            });
        }