/// <summary>
 /// Called when a Challenge causes a redirect to authorize endpoint in the Purecloud middleware
 /// </summary>
 /// <param name="context">Contains redirect URI and <see cref="AuthenticationProperties"/> of the challenge </param>
 public virtual void ApplyRedirect(PurecloudApplyRedirectContext context)
 {
     OnApplyRedirect(context);
 }
        protected override Task ApplyResponseChallengeAsync()
        {
            if (Response.StatusCode != 401)
            {
                return(Task.FromResult <object>(null));
            }

            AuthenticationResponseChallenge challenge = Helper.LookupChallenge(Options.AuthenticationType, Options.AuthenticationMode);

            if (challenge != null)
            {
                string baseUri =
                    Request.Scheme +
                    Uri.SchemeDelimiter +
                    Request.Host +
                    Request.PathBase;

                string currentUri =
                    baseUri +
                    Request.Path +
                    Request.QueryString;

                string redirectUri =
                    baseUri +
                    Options.CallbackPath;

                AuthenticationProperties properties = challenge.Properties;
                if (string.IsNullOrEmpty(properties.RedirectUri))
                {
                    properties.RedirectUri = currentUri;
                }

                // OAuth2 10.12 CSRF
                GenerateCorrelationId(Options.CookieManager, properties);

                // comma separated
                //string scope = string.Join(",", Options.Scope);

                string state = Options.StateDataFormat.Protect(properties);

                var cookieOptions = new CookieOptions
                {
                    HttpOnly = true,
                    Secure   = Request.IsSecure
                };

                Response.Cookies.Append(StateCookie, Options.StateDataFormat.Protect(properties), cookieOptions);

                string authorizationEndpoint =
                    Options.AuthorizationEndpoint +
                    "?response_type=code" +
                    "&client_id=" + Uri.EscapeDataString(Options.AppId) +
                    "&redirect_uri=" + Uri.EscapeDataString(redirectUri) +
                    "&state=" + Uri.EscapeDataString(state);

                var redirectContext = new PurecloudApplyRedirectContext(
                    Context, Options,
                    properties, authorizationEndpoint);
                Options.Provider.ApplyRedirect(redirectContext);
            }

            return(Task.FromResult <object>(null));
        }