Mvc: Detect session timeout in .net core

[rpundlik]

How can we detect session timeout in .net core and on detection redirect to login page ?

My application is multi tenant application, for which I am using sasskit library. So, after resolving the teanant I am keeping the TenantContext in session.
If my application goes into idle state and after that If I try to pull the data from database the it gives the TenantContext null is error and all its properties are null.
Below is my code
Startup

public void ConfigureServices(IServiceCollection services)
        {
            // Add multitenant
            services.AddMultitenancy<AppTenant, CachingAppTenantResolver>();

            services.Configure<Settings>(Configuration.GetSection("Settings"));

            // Add framework services.
            services.AddApplicationInsightsTelemetry(Configuration);

            // add Dbcontext 
            services.AddEntityFrameworkSqlServer().AddDbContext<LMSContext>();

            services.AddIdentity<ApplicationUser, ApplicationRole>()
                .AddEntityFrameworkStores<LMSContext, int>()
                .AddDefaultTokenProviders();

            services.AddMemoryCache();
            services.AddDistributedMemoryCache();
            services.AddSession(options =>
            {
                options.IdleTimeout = TimeSpan.FromHours(1);
            });

            services.AddSqlLocalization(options => options.UseTypeFullNames = true);
            services.AddOptions();
            services.AddMvc(o =>
            {
                o.Filters.Add(new LanguageActionFilter());
            })
            .AddViewLocalization()
            .AddDataAnnotationsLocalization()
            .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver());

            services.Configure<MultitenancyOptions>(Configuration.GetSection("Multitenancy"));

        }

public void Configure(IApplicationBuilder app, IHostingEnvironment env,   ILoggerFactory loggerFactory)
    {

        app.UseMultitenancy<AppTenant>();

    }
``````

public class LMSContext : IdentityDbContext
{
private readonly AppTenant tenant;

   public LMSContext(AppTenant tenant)
    {
        this.tenant = tenant;
    }

   protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {

        optionsBuilder.UseSqlServer(tenant.ConnectionString); // Here I am getting the tenant null

        base.OnConfiguring(optionsBuilder);
    }
}

Here not able to get it from session and thus the tenant is not injected in DBContext

protected override Task> ResolveAsync(HttpContext context)
{
string strPath = string.Empty;

        TenantContext<AppTenant> tenantContext = context.Session.GetObjectFromJson<TenantContext<AppTenant>>("TenantContext");

}
```
Any help on this appreciated !

[rynowak]

/cc @Tratcher @sebastienros

[Tratcher]

The short answer is that when you detect missing data / a new empty session then it's safe to assume the prior session timed out.

[hishamco]

@Tratcher what about checking the expiration in the data store IDistributedCache?

[Tratcher]

@hishamco the app doesn't have access to that information, it's maintained by the external store.

[hishamco]

I see, probably your previous suggestion is simple answer for the timeout

[rynowak]

Closing as this was answered here: https://github.com/aspnet/Mvc/issues/6126#issuecomment-293917933

[dougajmcdonald]

@rynowak here is here or not an object! :(

[nathanchere]

Closing as this was answered here: #6126 (comment)

This is not a necessarily correct answer in that there are other reasons why a new/empty session is returned (e.g. application restart without an external cache). I would also want to explicitly know when a session has timed out as opposed to simply losing session for other reasons, but I don't see a way to do it with the standard interfaces.