public void ConfigureServices( IServiceCollection services )
{

    services.AddDistributedMemoryCache();

    services.AddSession(options =>
    {
        // Set a short timeout for easy testing.
        options.IdleTimeout = TimeSpan.FromSeconds(10);
        options.Cookie.HttpOnly = true;
    });

    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);    
}


public void Configure( IApplicationBuilder app, IHostingEnvironment env )
{
    ....
    app.UseSession();
    app.UseMvc();
}

[HttpGet("sysinfo/akka")]
public String GetActorSystemInfo()
{            
    if (string.IsNullOrEmpty(HttpContext.Session.GetString("akkainfo")))
    {
        String systemInfo = _service.GetActorSystemInfo();
        HttpContext.Session.SetString( "akkainfo", String.Format("{0} == {1}", systemInfo,DateTime.Now) );
    }

    var systemInfo_cache = HttpContext.Session.GetString("akkainfo");

    return systemInfo_cache;
}