Asp.Net Core OnAuthenticationFailed

AspNetCore_Auth_OnAuthenticationFailed.cs

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<CookiePolicyOptions>(options =>
    {
        // ...
    });

    services.AddAuthentication(AzureADDefaults.AuthenticationScheme)
        .AddAzureAD(options => Configuration.Bind("AzureAd", options));

    // ...

    services.Configure<OpenIdConnectOptions>(AzureADDefaults.OpenIdScheme, options =>
    {
    options.Authority = options.Authority;

    // Token Validation
    options.TokenValidationParameters.IssuerValidator = AadIssuerValidator.ValidateAadIssuer;

    // Response type
    options.ResponseType = "id_token code";

    // On Authorization Code Received
    options.Events.OnAuthorizationCodeReceived = async context =>
    {
        // ...
    };

    // On Authentication Failed
    options.Events.OnAuthenticationFailed = async context =>
    {
        String ErrorMessage = context.Exception.Message;
        String InnerErrorMessage = String.Empty;

        String RedirectError = String.Format("?error_message={0}", ErrorMessage);

        if (context.Exception.InnerException != null)
        {
            InnerErrorMessage = context.Exception.InnerException.Message;
            RedirectError = String.Format("{0}&inner_error={1}", RedirectError, InnerErrorMessage);
        }

	 // or you can just throw it
	 // throw new Exception(RedirectError);

        RedirectError = RedirectError.Replace("\r\n", "  ");

        context.Response.Redirect(RedirectError);
        context.HandleResponse();
    };

    // ...