.NET Core 2.2 Shared Cookie causes Bad Request error when logging in

Question

I have 2 applications that share cookies between them. This is the configuration in both the startup.cs:

services.ConfigureApplicationCookie(options =>
{
    // Cookie settings
    options.Cookie.Name = Environment.GetEnvironmentVariable(CONST.CookieName);
    options.Cookie.SameSite = SameSiteMode.Lax;
    options.Cookie.SecurePolicy = CookieSecurePolicy.SameAsRequest;
    options.Cookie.Path = Environment.GetEnvironmentVariable(CONST.CookiePath);
    options.Cookie.Domain = Environment.GetEnvironmentVariable(CONST.CookieDomain);
    options.Cookie.HttpOnly = true;
    options.ExpireTimeSpan = TimeSpan.FromMinutes(Convert.ToDouble(Environment.GetEnvironmentVariable(CONST.CookieExpiryTimeSpanInMinutes)));

    options.LoginPath = Environment.GetEnvironmentVariable(CONST.LoginPath);
    options.AccessDeniedPath = Environment.GetEnvironmentVariable(CONST.AccessDeniedPath);
    options.SlidingExpiration = true;
});

The problem now is that if I load App A and App B together, login into App A then click login on App B, I get a Bad Request error. I tried to debug App B to check why it was getting this error and I discovered that when I am logged in to App A and try to login on App B, the Application doesn't know that I have already been authenticated.

if (User.Identity.IsAuthenticated)
{
    return LocalRedirect(returnUrl);
}

The line above is always false.

Is there a way to prevent this issue? Or is there a way to check if a cookie has already been set?

EDIT:

I have set the Data Protection Key for all the apps:

var ds = new DirectoryInfo("PathTOKey");
services.AddDataProtection()
    .PersistKeysToFileSystem(ds)
    .SetApplicationName("DPName");

EDIT:

Cookie Options in Startup.cs

services.Configure<CookiePolicyOptions>(options =>
{
    // This lambda determines whether user consent for non-essential cookies is needed for a given request.
    options.CheckConsentNeeded = context => false;
    options.MinimumSameSitePolicy = SameSiteMode.None;
});
services.Configure<IdentityOptions>(options =>
{
    options.Password.RequireDigit = false;
    options.Password.RequireLowercase = false;
    options.Password.RequireNonAlphanumeric = true;
    options.Password.RequireUppercase = true;
    options.Password.RequiredLength = 6;
    options.User.AllowedUserNameCharacters =
    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._@+";
    options.User.RequireUniqueEmail = false;
    options.SignIn.RequireConfirmedEmail = false;
    options.SignIn.RequireConfirmedPhoneNumber = false;
    options.Lockout.AllowedForNewUsers = false;
});
var ds = new DirectoryInfo(Path.Combine(Environment.GetEnvironmentVariable(UCCASGlobals.CentralApplicationSettings), "KeyRing"));
services.AddDataProtection()
    .PersistKeysToFileSystem(ds)
    .SetApplicationName(Environment.GetEnvironmentVariable(UCCASGlobals.DataProtectionApplicationName));

services.ConfigureApplicationCookie(options =>
{
    // Cookie settings
    options.Cookie.Name = Environment.GetEnvironmentVariable(UCCASGlobals.CookieName);
    options.Cookie.SameSite = SameSiteMode.Lax;
    options.Cookie.SecurePolicy = CookieSecurePolicy.SameAsRequest;
    options.Cookie.Path = Environment.GetEnvironmentVariable(UCCASGlobals.CookiePath);
    options.Cookie.Domain = Environment.GetEnvironmentVariable(UCCASGlobals.CookieDomain);
    options.Cookie.HttpOnly = true;
    options.ExpireTimeSpan = TimeSpan.FromMinutes(Convert.ToDouble(Environment.GetEnvironmentVariable(UCCASGlobals.CookieExpiryTimeSpanInMinutes)));

    options.LoginPath = Environment.GetEnvironmentVariable(UCCASGlobals.LoginPath);
    options.AccessDeniedPath = Environment.GetEnvironmentVariable(UCCASGlobals.AccessDeniedPath);
    options.SlidingExpiration = true;
});

Answer 1

Make sure that you have configured data protection in both of application and data protection keys and the app name must be the same in two Apps .

Configures the data protection system to persist keys to the specified directory. This path may be on the local machine or may point to a UNC share.

services.AddDataProtection()
         .PersistKeysToFileSystem(new DirectoryInfo(@"d:\Keys"))
         .SetApplicationName("SharedCookieApp");

services.ConfigureApplicationCookie(options => {
          options.Cookie.Name = ".AspNet.SharedCookie";
        });

You could check the cookies value by cookie name in the request

var cookie=Request.Cookies["Cookie Name"];

Reference : https://learn.microsoft.com/en-us/aspnet/core/security/data-protection/configuration/overview?view=aspnetcore-3.0