Ajout au fichier Startup.auth.cs pour gérer l'exception levée en cas d'authentification refusée

addToStartup.auth.cs

app.UseOpenIdConnectAuthentication(
                new OpenIdConnectAuthenticationOptions
                {
                    ...

                    Notifications = new OpenIdConnectAuthenticationNotifications()
                    {
                        // If there is a code in the OpenID Connect response, redeem it for an access token and refresh token, and store those away.
                       AuthorizationCodeReceived = (context) => 
                       {
                           ...
                       },

                       AuthenticationFailed = (context) =>
                       {
                           // FR: on construit l'URL de redirection (https://secretplansmark48.azurewebsites.net/Access/Denied/)
                           // EN: we build the URL to redirect to (https://secretplansmark48.azurewebsites.net/Access/Denied/)
                           string url = context.Request.Scheme + "://" + context.Request.Host + "/Access/Denied/";
                           context.ProtocolMessage.RedirectUri = url;

                           // FR: on force la redirection vers l'URL qu'on a construit
                           // EN: we force the redirect to the URL we've built
                           context.HandleResponse();
                           context.Response.Redirect(context.ProtocolMessage.RedirectUri);

                           return Task.FromResult(0);
                       }
                    }
                });