How to fix "The SSL connection could not be established, see inner exception." when trying to download osu! avatar

Question

I want to download osu! avatars to use them, but keep getting this error:

The SSL connection could not be established.

Inner exception is:

System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception. ---> System.Security.Authentication.AuthenticationException: Authentication failed, see inner exception. ---> System.ComponentModel.Win32Exception: Получено непредвиденное сообщение или оно имеет неправильный формат

Example url: https://a.ppy.sh/10638551?1524507784.png

I tried using HttpClient and WebClient but without any success.

using(HttpClient client = new HttpClient())
{
     var resp = await client.GetAsync("https://a.ppy.sh/10638551?1547998515.jpeg");
     var responseStr = await resp.Content.ReadAsStringAsync();
     File.WriteAllText("html/avatars/avatar.jpeg", responseStr);
}

Answer 1

I found te solution this blog helped me

ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, errors) =>
{
    // local dev, just approve all certs
    if (development) return true;
    return errors == SslPolicyErrors.None ;
};

https://www.khalidabuhakmeh.com/validate-ssl-certificate-with-servicepointmanager

Answer 2

Before use HttpClient you should setup HttpClientHandler;

var handler = new HttpClientHandler();

handler.ServerCertificateCustomValidationCallback += 
                (sender, certificate, chain, errors) =>
                {
                    return true;
                };

only than your HttpClient code. Must Work for .net Core 3.*