/// <summary>
        /// Adds the <see cref="YoukuMiddleware"/> middleware to the specified <see cref="IApplicationBuilder"/>, which enables Youku authentication capabilities.
        /// </summary>
        /// <param name="app">The <see cref="IApplicationBuilder" /> to add the middleware to.</param>
        /// <param name="configureOptions">An action delegate to configure the provided <see cref="YoukuOptions"/>.</param>
        /// <returns>A reference to this instance after the operation has completed.</returns>
        public static IApplicationBuilder UseYoukuAuthentication(this IApplicationBuilder app, Action <YoukuOptions> configureOptions)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            var options = new YoukuOptions();

            configureOptions?.Invoke(options);
            return(app.UseYoukuAuthentication(options));
        }
        /// <summary>
        /// Adds the <see cref="YoukuMiddleware"/> middleware to the specified <see cref="IApplicationBuilder"/>, which enables Youku authentication capabilities.
        /// </summary>
        /// <param name="app">The <see cref="IApplicationBuilder" /> to add the middleware to.</param>
        /// <param name="options">A <see cref="YoukuOptions"/> that specifies options for the middleware.</param>
        /// <returns>A reference to this instance after the operation has completed.</returns>
        public static IApplicationBuilder UseYoukuAuthentication(this IApplicationBuilder app, YoukuOptions options)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            return(app.UseMiddleware <YoukuMiddleware>(options));
        }