public async Task SignTextAsync(AuthRequest authRequest) 
        {
            X509Store store = new X509Store("MY", StoreLocation.CurrentUser);
            store.Open(OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);

           X509Certificate2 certificate=default;

            foreach (var cert in store.Certificates) // ищем нужный нам сертификат
            {
                if (string.Equals(cert.SerialNumber, "012345679"))
                {
                   certificate = cert;         
                    break;
                }
            }

            if (certificate is null)
                throw new Exception("Не найден сертификат");

            UnicodeEncoding encoding = new UnicodeEncoding();

            byte[] data = encoding.GetBytes(authRequest.data); //authRequest.data is string

            if (!certificate.HasPrivateKey)
               throw  new Exception("У сертификата нет приватного ключа");

            RSACryptoServiceProvider provider= (RSACryptoServiceProvider)certificate.PrivateKey; //System.NotSupportedException: The certificate key algorithm is not supported        
        }

 provider.SignData(dataToBeSigned, new SHA1CryptoServiceProvider());

           var re= certificate.GetDSAPrivateKey();
            var go = certificate.GetECDsaPrivateKey();
            var re1 = certificate.GetRSAPrivateKey();