What is the role of the cookie middleware in SPA Template - visual-studio-2013

Question

The VS 2013 SPA Template is configured with the cookie middleware, among other middlewares like the OAuth MW or ExternalCookie MW.
// Enable the application to use a cookie to store information for the signed in user
app.UseCookieAuthentication(new CookieAuthenticationOptions
{
AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
LoginPath = new PathString("/Account/Login"),
Provider = new CookieAuthenticationProvider
{
OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
validateInterval: TimeSpan.FromMinutes(20),
regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
}
});
// Use a cookie to temporarily store information about a user logging in with a third party login provider
app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);
// Enable the application to use bearer tokens to authenticate users
app.UseOAuthBearerTokens(OAuthOptions);
Since the WebApi will authorize the calls made from the client side through bearer tokens and the external cookie middleware is there to support external login providers, what role does the cookie middleware serve in this?

Answer 1

It's there as a replacement for forms authentication. Before, a user would sign in with forms auth, then it would issue a cookie, and create a principal object that represents the user's identity. With OWIN, the cookie authentication middleware does the same task.
It will also handle things like logins/redirects (forbidden requests) as you can see with the above line of code:
LoginPath = new PathString("/Account/Login"),