"The SSL connection could not be established, see inner exception." For POST Request(.net 6)

Question

First of all the title of the question may seem like a duplicate. But I tried all possible solutions at SO and nothing works. Most interestingly the same code is working for .net framework-4.x.

The certificate and the key is valid as the same code with same .crt and .key is working.

var certPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/"), "othoba.crt");
var keyPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/"), "othoba.key");
    
    
string certificateText = File.ReadAllText(certPath);
string privateKeyText = File.ReadAllText(keyPath);
    
    
    
ICertificateProvider provider = new CertificateFromFileProvider(certificateText, privateKeyText, true);
    
var certificate = provider.Certificate;
string accessTokenUrl = string.Empty;
accessTokenUrl = "https://sandbox.thecitybank.com:7788/transaction/token";
    
    
var handler = new HttpClientHandler();
handler.ClientCertificates.Add(certificate);
handler.ServerCertificateCustomValidationCallback +=(sender, certificate, chain, errors) => {
                        return true;
                    };
string json = JsonConvert.SerializeObject(new
{
   userName = _cityBankPaymentSettings.UserName,
   password = _cityBankPaymentSettings.Password
});
var httpContent = new StringContent(json, Encoding.UTF8, "application/json");    
var client = new HttpClient(handler);
var result = client.PostAsync(accessTokenUrl, httpContent).GetAwaiter().GetResult();

Answer 1

          try
            {
                var pfxPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/"), "othoba.pfx");
                var certPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/SandBoxCrt/"), "othoba.crt");
                var keyPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/SandBoxCrt/"), "othoba.key");


                string tokenUrl = "https://ecomm-webservice.thecitybank.com:7788/transaction/token";
                string crtPassword = _cityBankPaymentSettings.CrtPasswordProduction;

                if (!_cityBankPaymentSettings.ProductionMode)
                {
                    tokenUrl = "https://sandbox.thecitybank.com:7788/transaction/token";
                    crtPassword = _cityBankPaymentSettings.CrtPasswordSandBox;
                    pfxPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/SandBoxCrt/"), "createorder.pfx");
                    certPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/SandBoxCrt/"), "createorder.crt");
                    keyPath = _fileProvider.Combine(_fileProvider.MapPath("~/Plugins/Payments.CityBankApi/SandBoxCrt/"), "createorder.key");

                }

                var certificate = await LoadPemCertificate(certPath, keyPath);
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
                var handler = new HttpClientHandler();
                handler.ClientCertificates.Add(certificate);
                handler.ServerCertificateCustomValidationCallback = (e, r, c, n) => true;

                string json = JsonConvert.SerializeObject(new
                {
                    userName = _cityBankPaymentSettings.UserName,
                    password = _cityBankPaymentSettings.Password
                });
                var httpContent = new StringContent(json, Encoding.UTF8, "application/json");
                var client = new HttpClient(handler);
                var result = await client.PostAsync(tokenUrl, httpContent);
                var jsonString = await result.Content.ReadAsStringAsync();
                cityBankAccessToken = JsonConvert.DeserializeObject<CityBankAccessTokenResponeModel>(jsonString);

                await _logger.InformationAsync("cityBankAccessToken:" + cityBankAccessToken);

            }
            catch (Exception ex)
            {
                await _logger.ErrorAsync("CityResponseAccessTokenExc:" + ex.Message, ex);
            }

Load Certificate method.

  public async Task<X509Certificate2> LoadPemCertificate(string certificatePath, string privateKeyPath)
        {
            using var publicKey = new X509Certificate2(certificatePath);

            var privateKeyText = await File.ReadAllTextAsync(privateKeyPath);
            var privateKeyBlocks = privateKeyText.Split("-", StringSplitOptions.RemoveEmptyEntries);
            var privateKeyBytes = Convert.FromBase64String(privateKeyBlocks[1]);
            using var rsa = RSA.Create();

            if (privateKeyBlocks[0] == "BEGIN PRIVATE KEY")
            {
                rsa.ImportPkcs8PrivateKey(privateKeyBytes, out _);
            }
            else if (privateKeyBlocks[0] == "BEGIN RSA PRIVATE KEY")
            {
                rsa.ImportRSAPrivateKey(privateKeyBytes, out _);
            }

            var keyPair = publicKey.CopyWithPrivateKey(rsa);
            var Certificate = new X509Certificate2(keyPair.Export(X509ContentType.Pfx));

            return Certificate;
        }

For Linux(Ubuntu 20.04)

Adding this to the top of /etc/ssl/openssl.cnf:

openssl_conf = default_conf
and this to the bottom of it:

[default_conf]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT:@SECLEVEL=1

helpful link