public async Task <IActionResult> Login(LoginInputModel model, string button)
        {
            // check if we are in the context of an authorization request
            var context = await _interaction.GetAuthorizationContextAsync(model.ReturnUrl);

            // the user clicked the "cancel" button
            if (button != "login")
            {
                if (context != null)
                {
                    // if the user cancels, send a result back into IdentityServer as if they
                    // denied the consent (even if this client does not require consent).
                    // this will send back an access denied OIDC error response to the client.
                    await _interaction.GrantConsentAsync(context, ConsentResponse.Denied);

                    // we can trust model.ReturnUrl since GetAuthorizationContextAsync returned non-null
                    if (await _clientStore.IsPkceClientAsync(context.ClientId))
                    {
                        // if the client is PKCE then we assume it's native, so this change in how to
                        // return the response is for better UX for the end user.
                        return(View("Redirect", new RedirectViewModel {
                            RedirectUrl = model.ReturnUrl
                        }));
                    }

                    return(Redirect(model.ReturnUrl));
                }
                else
                {
                    // since we don't have a valid context, then we just go back to the home page
                    return(Redirect("~/"));
                }
            }

            if (ModelState.IsValid)
            {
                if (await _usersService.AreUserCredentialsValidAsync(model.Username, model.Password))
                {
                    var user = await _usersService.GetUserByUsernameAsync(model.Username);

                    // 2-F.A
                    var id = new ClaimsIdentity();
                    id.AddClaim(new Claim(JwtClaimTypes.Subject, user.SubjectId));
                    await HttpContext.SignInAsync(scheme : Startup.TwoFactorAuthenticationScheme,
                                                  principal : new ClaimsPrincipal(id));

                    await _twoFactorAuthenticationService.SendTemporaryCodeAsync(user.SubjectId);

                    var redirectToAdditionalFactorUrl =
                        Url.Action("AdditionalAuthenticationFactor",
                                   new
                    {
                        returnUrl     = model.ReturnUrl,
                        rememberLogin = model.RememberLogin
                    });

                    // request for a local page
                    if (Url.IsLocalUrl(model.ReturnUrl))
                    {
                        //return Redirect(model.ReturnUrl);
                        return(Redirect(redirectToAdditionalFactorUrl));
                    }

                    if (string.IsNullOrEmpty(model.ReturnUrl))
                    {
                        return(Redirect("~/"));
                    }

                    // user might have clicked on a malicious link - should be logged
                    throw new Exception("invalid return URL");
                }

                await _events.RaiseAsync(new UserLoginFailureEvent(model.Username, "invalid credentials"));

                ModelState.AddModelError("", AccountOptions.InvalidCredentialsErrorMessage);
            }

            // something went wrong, show form with error
            var vm = await BuildLoginViewModelAsync(model);

            return(View(vm));
        }