Sharing Auth Cookies between .NET 4.6.1 and NET Core (Cookies was not authenticated. Failure message: Unprotect ticket failed)

I’m having an incredibly difficult time getting auth cookies made in .NET 4.6.1 to work in .NET Core. I followed online microsoft documentation, but have not had any successs ( https://docs.microsoft.com/en-us/aspnet/core/security/cookie-sharing?view=aspnetcore-2.1 )

I have a site url like site1.mysite.local that is in 4.6.1 and site2.mysite.local which is a .NET Core 2.1 site

I added the following code to the startup class of .NET 4.6.1 (site1.mysite.local). I also changed the constant values to string values to make it easier to follow in the examples below.

var cookieEncryptionKeyRing = "C:/Keyring";

var authOptions = new CookieAuthenticationOptions
{
    CookieName = "theCookieName",
    CookieDomain = ".mysite.local",
    AuthenticationType = "Cookies",
    LoginPath = new PathString("/default.aspx"),
    LogoutPath = new PathString("/logout.aspx"),
    ExpireTimeSpan = TimeSpan.FromMinutes(Convert.ToDouble(20)),
    SlidingExpiration = true,

    Provider = new CookieAuthenticationProvider()
    {
        OnValidateIdentity = (cic) => {
            // Validate token and / or refresh it.                        
            return Task.FromResult<object>(true);
        },
    },
    TicketDataFormat = new AspNetTicketDataFormat(
        new DataProtectorShim(
            DataProtectionProvider.Create(new DirectoryInfo(cookieEncryptionKeyRing),
                    (builder) => { builder.SetApplicationName("SharedCookieApp"); })
                .CreateProtector(
                    "Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware",
                    "Cookies",
                    "v2"))),
    CookieManager = new ChunkingCookieManager()
};

app.UseCookieAuthentication(authOptions);
app.SetDefaultSignInAsAuthenticationType("Cookies");

This works well for the .NET 4.6.1 (site1.mysite.local) web app. I am able to log in and use the cookie to maintain authentication within site1.mysite.local.

This doesn’t work in the NET Core app and I get the error message “Cookies was not authenticated. Failure message: Unprotect ticket failed”

I added the following code to the startup class of .NET Core (site2.mysite.local).

public void ConfigureServices(IServiceCollection services)
{
    var keyRing = "C:/Keyring";

    var protectionProvider = DataProtectionProvider.Create(
        new DirectoryInfo(keyRing), (action) =>
        {
            action.SetApplicationName("SharedCookieApp");
        });
    var dataProtector = protectionProvider.CreateProtector(
        "Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware",
        "Cookies",
        "v2");
    var ticketFormat = new TicketDataFormat(dataProtector);

    services.AddAuthentication("Cookies")
        .AddCookie(CookieAuthenticationDefaults.AuthenticationScheme, options =>
        {
            options.LoginPath = "/Home/AccessDenied";
            options.Cookie.Name = "theCookieName";    
            options.Cookie.Domain = ".mysite.local";
            options.TicketDataFormat = ticketFormat;
            options.Events.OnValidatePrincipal = (cic) =>
            {
                return Task.FromResult<object>(true);
            };
        });

    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseHsts();
    }

    app.UseHttpsRedirection();
    app.UseStaticFiles();            
    app.UseAuthentication();
    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

I’ve gone over all the documentation I’ve been able to find and nothing has given me any clue on what to do.

Any help you can give would be greatly appreciated. Thank you!