MVC 5 Identity (v2) Authentication Without Creating an Application User - asp.net-mvc

Question

Is there a way to authenticate a session without creating an ApplicationUser in MVC 5 identity?
For various reasons, I ended up using a two layered authentication system. I parse a "user" object from my custom db into session, and in various places all over the site, the existence of this object is how the logged-in status of a user is determined.
I use Identity user stuff (e.g. claims, logins, etc.) at various places of the site. But at this one specific instance, I need to log in an anonymous Identity user and parse whatever user object is requested to the session. So how can I create an anonymously authenticated session with Identity V2?

Answer 1

In Identity you don't need to have user object to authenticate. You could create some claims on the fly and use them to authenticate. Consider this simple example:
[HttpPost]
public ActionResult AnonymousLogin()
{
var ident = new ClaimsIdentity(
new[]
{
// adding following 2 claim just for supporting default antiforgery provider
new Claim(ClaimTypes.NameIdentifier, "AnonymousUserID"),
new Claim("http://schemas.microsoft.com/accesscontrolservice/2010/07/claims/identityprovider", "ASP.NET Identity", "http://www.w3.org/2001/XMLSchema#string"),
new Claim(ClaimTypes.Name, "AnonymousUserID"),
},
DefaultAuthenticationTypes.ApplicationCookie);
HttpContext.GetOwinContext().Authentication.SignIn(
new AuthenticationProperties { IsPersistent = false }, ident);
return RedirectToAction("MyAction"); // auth succeed
}
Now you have authenticated an anonymous user just like a real user:
[Authorize]
public ActionResult MyAction()
{
// all authorized users could use this method don't matter how have been authenticated
// you have access current user principal
var username=HttpContext.User.Identity.Name;
}