public HttpResponseMessage PostLoginUser(UserModel model)
        {
            return this.PerformOperationAndHandleExceptions(() =>
            {
                var context = new BankContext();
                using (context)
                {
                    var usernameToLower = model.Username.ToLower();
                    var entity = context.Users.SingleOrDefault(u => u.Username == usernameToLower &&
                        u.AuthCode == model.AuthCode);
                    if (entity == null)
                    {
                        var errResponse = this.Request.CreateErrorResponse(HttpStatusCode.BadRequest,
                            "Invalid username or password");
                        throw new HttpResponseException(errResponse);
                    }

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

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

                    var response = this.Request.CreateResponse(HttpStatusCode.Accepted, responseModel);
                    return response;
                }
            });
        }
        public HttpResponseMessage Login(UserModel model)
        {
            var responseMsg = this.ExceptionHandling(
              () =>
              {
                  var context = new BankContext();
                  using (context)
                  {
                      this.ValidateUsername(model.Username);
                      this.ValidateAuthCode(model.AuthCode);
                      var usernameToLower = model.Username.ToLower();
                      var user = context.Users.FirstOrDefault(
                          usr => usr.Username == usernameToLower
                          && usr.AuthCode == model.AuthCode);

                      if (user == null)
                      {
                          throw new InvalidOperationException("Invalid username or password!");
                      }
                      if (user.SessionKey == null)
                      {
                          user.SessionKey = this.GenerateSessionKey(user.Id);
                          context.SaveChanges();
                      }

                      var loggedModel = new LoggedUserModel()
                      {
                          Username = user.Username,
                          SessionKey = user.SessionKey
                      };

                      var response =
                          this.Request.CreateResponse(HttpStatusCode.Created,
                                          loggedModel);
                      return response;
                  }
              });

            return responseMsg;
        }
        public HttpResponseMessage PostRegisterUser(UserModel model)
        {
            return this.PerformOperationAndHandleExceptions(() =>
            {
                var usernameToLower = model.Username.ToLower();
                var context = new BankContext();
                using (context)
                {
                    var entity = context.Users.FirstOrDefault(u => u.Username == usernameToLower);
                    if (entity != null)
                    {
                        string responseMessage = "Username already taken";

                        HttpResponseMessage errResponse =
                            this.Request.CreateErrorResponse(HttpStatusCode.Conflict, responseMessage);
                        throw new HttpResponseException(errResponse);
                    }

                    var user = new User()
                    {
                        Username = model.Username.ToLower(),
                        AuthCode = model.AuthCode
                    };

                    context.Users.Add(user);
                    context.SaveChanges();
                    return this.PostLoginUser(model);
                }
            });
        }