Security: Get message "Unexpected token <" when trying to approve content after logout

Description

Steps to reproduce

1. UserA is approver of content 1, and Content is in review state.
2. Open the site in 2 tabs of a browser: Content 1 is opening on OPE mode in both browsers.
3. On tab 1: User logs out of site.
4. On tab 2: User opens the option menu then clicks Approve changes.

Expected:
Show dialog requiring user to log in again.

Actual:
Show dialog with message "Unexpected token <"

How to apply:

If you are using the our standard Asp.net Identity setup in Startup, you also need to hook up a new handler to the OnApplyRedirect on the Provider object. app.CmsOnCookieApplyRedirect...

// Use cookie authentication
            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
                LoginPath = new PathString(Global.LoginPath),
                Provider = new CookieAuthenticationProvider
                {
                    // If the "/util/login.aspx" has been used for login otherwise you don't need it you can remove OnApplyRedirect.
                    OnApplyRedirect = cookieApplyRedirectContext =>
                    {
                        app.CmsOnCookieApplyRedirect(cookieApplyRedirectContext, cookieApplyRedirectContext.OwinContext.Get<ApplicationSignInManager<ApplicationUser>>());
                    },
 
                    // 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>, ApplicationUser>(
                        validateInterval: TimeSpan.FromMinutes(30),
                        regenerateIdentity: (manager, user) => manager.GenerateUserIdentityAsync(user))
                }
            });