OWIN Authentication Cookie

I’ve been struggling with OWIN cookies for a couple of days now and I’m hoping someone can point me in the right direction.

I want my users to be logged out only when the browser is closed. I’ve tried everything I can think of, but I can’t prevent users from being logged out after 20 minutes.

These are my relevant web.config settings

<system.web><authentication mode="None" />    </system.web><system.webServer><modules><remove name="FormsAuthentication" /></modules></system.webServer>

This is my Startup class.

    public partial class Startup
    {
        public void ConfigureAuth(IAppBuilder app)
        {
            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
                LoginPath = new PathString("/account/login"),
                AuthenticationMode = Microsoft.Owin.Security.AuthenticationMode.Active,
                CookieSecure = CookieSecureOption.SameAsRequest,
                CookieHttpOnly = true,
                SlidingExpiration = false,
                LogoutPath = new PathString("/account/login")
            });
        }
    }

What causes the early expiration? 

Can anyone suggest what I'm doing wrong?