Tenant redirect for IS3

AcrHelper.cs

    public class AcrHelper
    {
        public static string GetAcrValue(IEnumerable<string> acrValues, string acrKey)
        {
            acrKey = string.Format("{0}:", acrKey);
            var acrKeyValue = acrValues.SingleOrDefault(x => x.StartsWith(acrKey));
            if (acrKeyValue == null) return null;
            var acrValue = acrKeyValue.Substring(acrKey.Length);
            return acrValue;
        }

        public static IEnumerable<string> FromSpaceSeparatedString(string input)
        {
            input = input.Trim();
            return input.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
        }
    }

Startup.cs

    public class Startup
    {
        public const string AppRoot = "/core";
        public void Configuration(IAppBuilder app)
        {
            app.Map(AppRoot, delegate(IAppBuilder coreApp)
            {
                coreApp.Use(InterceptNoTenant);
                coreApp.UseIdentityServer(...);
            });
        }
        private static async Task InterceptNoTenant(IOwinContext env, Func<Task> next)
        {
            var pathMatch = new PathString("/connect/authorize");
            try
            {
                var path = env.Request.Path;
                PathString remainingPath;
                if (path.StartsWithSegments(pathMatch, out remainingPath))
                {
                    // If we have a query string
                    if (env.Request.QueryString.HasValue)
                    {
                        // Parse it and find the acr_values.
                        var queryString = HttpUtility.ParseQueryString(env.Request.QueryString.Value);
                        string value;
                        if (!String.IsNullOrWhiteSpace(queryString.Get("setcookie")))
                        {
                            await next();
                            return;
                        }
                        if (!String.IsNullOrWhiteSpace((value = queryString.Get("acr_values"))))
                        {
                            // Find the tenant in the values.
                            var acr = AcrHelper.FromSpaceSeparatedString(value);
                            var tenant = AcrHelper.GetAcrValue(acr, "tenant");
                            if (!String.IsNullOrWhiteSpace(tenant))
                            {
                                // Set the cookie and continue authentication.
                                TenantHelper.SetCookie(env, tenant);
                                var url = env.Request.Uri.AddParameter("setcookie", "true");
                                env.Response.Redirect(url.ToString());
                                return;
                            }
                        }
                    }
                    // Check the cookie
                    if (!TenantHelper.HasCookie(env))
                    {
                        // If no cookie, then redirect to tenant select.
                        var url = env.Request.PathBase.Add(new PathString("/tenant")).Add(new QueryString("returnUrl", env.Request.Uri.ToString()));
                        env.Response.Redirect(url);
                        return;
                    }
                    // Here, we should have a cookie set
                }
            }
            catch (Exception ex)
            {
                Logger.Error("Failed to intercept client with no tenant", ex);
            }
            await next();
        }
    }

TenantHelper.cs

    public class TenantHelper
    {
        public const string CookieA = "CookieA";
        public static bool HasCookie(IOwinContext context) {
            return !String.IsNullOrWhiteSpace(context.Request.Cookies[CookieA]);
        }
        public static void SetCookie(IOwinContext context, string cookieValue)
        {
            context.Response.Cookies.Append(CookieA, cookieValue, new CookieOptions()
            {
                Expires = DateTime.Today.AddDays(30),
                HttpOnly = true,
                Secure = true
            });
        }
    }