retrive Claims in a Single Sign On sulotion using Identity 2

We have three ASP.NET MVC 5 projects working alongside. for authentication, we came up using Single Sign On, following the very simple tutorial bellow:

Implementation of Single Sign On (SSO) in ASP.NET MVC

The main idea is to create a MachineKey shared between 3, and add the same authentication settings in 3 web.config files.

So now we have 3 sites called:

• SSO
• WebApp1
• WebApp2

one of our projects (SSO) does the job and two other depend on it. It works and we were happy but...

We are using Identity 2 Claim Based authentication in the SSO project and when a user logs in, we add some custom claims to his "identity". this way, we have 2 separate cookies: one for Single Sign On process and one for saving claims. here is the c# code:

[HttpPost]
    [AllowAnonymous]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> Login(LoginViewModel model, string fromSite, string returnUrl)
    {
        if (!ModelState.IsValid)
        {
            return View(model);
        }

        var result = await SignInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, shouldLockout: false);
        switch (result)
        {
            case SignInStatus.Success:
                // here the cookie which contains claims *is created* by Identity 2

                // here we create the cookie used for Single Sing On
                FormsAuthentication.SetAuthCookie(username, false);

                // redirecting
                if (string.IsNullOrWhiteSpace(fromSite))
                {
                    if (string.IsNullOrWhiteSpace(returnUrl)) return RedirectToAction("Index", "Home");
                    return RedirectToLocal(returnUrl);
                }

                return Redirect(string.Format("{0}{1}", fromSite, returnUrl));

                // other cases inside switch
                .
                .
                .
        }
    }

When a user goes from SSO site to another, say WebApp1, it remains logged in but we lost claims. Is there any way to "merge" these 2 cookies and retrive the claims in another site?