Get cookies from external website after authentication

Hi All,

I have been a C++ developer all my life. So i am new to asp.net and web technologies as such. 

I need to develop a small cross-platform application, which will basically open an external website. And allow the user to sign-in (username and password). Once the user is authenticated, this application needs to fetch the cookies and hand it over to a C++ desktop application. It is basically SSO credentials, so the website redirects to a page where the authentication happens.

For this, i have written some code, which for now opens the website. But i am cluless on how to get the cookies and hand it over to the C++ app.

//Program.cs 

class Program
{

    static void Main(string[] args)
    {
        var host = new WebHostBuilder()
       .UseKestrel()
       .UseStartup<Startup>()
       .Build();

        host.Start();
        OpenBrowser("https://mywebsite.com/auth/samlsso.php");
    }

    public static void OpenBrowser(string url)
    {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            Process.Start(new ProcessStartInfo("cmd", $"/c start {url}"));
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
        {
            Process.Start("xdg-open", url);
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
        {
            Process.Start("open", url);
        }
        else
        {
            // throw 
        }
    }
}   

 //startup.cs

namespace SampleCore
{
    public class Startup
    {
        public void Configure(IApplicationBuilder builder)
        {
            builder.Run(appContext =>
            {
                return appContext.Response.WriteAsync("Hey, I'm from Web!");
            });
        }
    }
}