/// <summary>
        /// Adds the <see cref="MailChimpAuthenticationMiddleware"/> middleware to the specified
        /// <see cref="IApplicationBuilder"/>, which enables MailChimp authentication capabilities.
        /// </summary>
        /// <param name="app">The <see cref="IApplicationBuilder"/> to add the middleware to.</param>
        /// <param name="options">A <see cref="MailChimpAuthenticationOptions"/> that specifies options for the middleware.</param>
        /// <returns>A reference to this instance after the operation has completed.</returns>
        public static IApplicationBuilder UseMailChimpAuthentication(
            [NotNull] this IApplicationBuilder app,
            [NotNull] MailChimpAuthenticationOptions options)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

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

            return(app.UseMiddleware <MailChimpAuthenticationMiddleware>(Options.Create(options)));
        }
        /// <summary>
        /// Adds the <see cref="MailChimpAuthenticationMiddleware"/> middleware to the specified
        /// <see cref="IApplicationBuilder"/>, which enables MailChimp authentication capabilities.
        /// </summary>
        /// <param name="app">The <see cref="IApplicationBuilder"/> to add the middleware to.</param>
        /// <param name="configuration">An action delegate to configure the provided <see cref="MailChimpAuthenticationOptions"/>.</param>
        /// <returns>A reference to this instance after the operation has completed.</returns>
        public static IApplicationBuilder UseMailChimpAuthentication(
            [NotNull] this IApplicationBuilder app,
            [NotNull] Action <MailChimpAuthenticationOptions> configuration)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

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

            var options = new MailChimpAuthenticationOptions();

            configuration(options);

            return(app.UseMiddleware <MailChimpAuthenticationMiddleware>(Options.Create(options)));
        }