How to stop Web API getting 401 when using OWIN Cookie authentication - angularjs

Question

I have a web app which is MVC 5 using OWIN cookie authentication. It also uses AngularJS from which web api calls are made. The Angular code is only invoked after the user has successfully logged in and been authenticated and everything works as you would expect.
However, can someone please explain what component (Chrome, OWIN, IIS, ...) is responsible for eventually issuing a 401 if the user has been idle for 20 or so minutes. In MVC this is not a problem because the redirect automatically re-authenticates but with web api my only option is to get the user to log back in again.
Ok so thats the first thing, who is responsible for timing the session out and giving the 401 (and can i alter it) but ALSO is there any way to get web api calls to keep the session alive so that even if the user is idle the api calls stop it timing out?
Specifically, I have implemented SignalR in a way that the signal to the client results in the client issuing an api call to refresh its data. I realise i could push the refresh but at the moment thats a bit tricky. So whats happening is the updates are occuring nicely but eventually this results in a 401 which i want to avoid.

Answer 1

below is an ideal flow
server logs in => creates cookie sets expiration time, passes it to client
client saves cookies & passes it with each request
server checks the cookies for validity including expiration time
if invalid or expired, server responds with 401

Answer 2

the cookie expiration time can be configured in the CookieAuthenticationOptions. See file ~/App_Start/Startup.Auth.cs
app.UseCookieAuthentication(new CookieAuthenticationOptions
{
ExpireTimeSpan=TimeSpan.FromDays(365),
AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
LoginPath = new PathString("/Account/Login"),
Provider = new CookieAuthenticationProvider
{
// Enables the application to validate the security stamp when the user logs in.
// This is a security feature which is used when you change a password or add an external login to your account.
OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
validateInterval: TimeSpan.FromMinutes(30),
regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
}
});
Set your ExpireTimeSpan to the desired TimeSpan.
For web api calls that fail authentication you could catch 401's and send back a response that tells the browser it's logged out - you could pop up a login dialog or redirect to login url.