(DOCSP-7887): added csharp x509 code (#577)

Author: Mohammad Hunan Chughtai

source/includes/connection-snippets/x509-snippets/csharp-connection.cs

@@ -0,0 +1,51 @@
+// begin x509 connection
+using MongoDB.Bson;
+using MongoDB.Driver;
+using System;
+using System.IO;
+using System.Threading.Tasks;
+using System.Collections.Generic;
+using System.Security.Cryptography.X509Certificates;
+
+// Tested using MongoDB.Driver 2.9.2 and netcoreapp 2.2
+
+namespace WorkingWithMongoDB
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            MainAsync().Wait();
+        }
+
+        static async Task MainAsync()
+        {
+            var connectionString = "mongodb+srv://<cluster-url>/test?authSource=$external&retryWrites=true&w=majority&authMechanism=MONGODB-X509";
+            var settings = MongoClientSettings.FromConnectionString(connectionString);
+
+            // You will need to convert your Atlas-provided PEM containing the cert/private keys into a PFX
+            // use openssl and the following line to create a PFX from your PEM:
+            // openssl pkcs12 -export -in <x509>.pem -inkey <x509>.pem -out <x509>.pfx -certfile <x509>.pem
+            // and provide a password, which should match the second argument you pass to X509Certificate2
+            var cert = new X509Certificate2("/etc/certs/mongodb/client-certificate.pfx", "<pfx_passphrase>");
+
+            settings.SslSettings = new SslSettings
+            {
+                ClientCertificates = new List<X509Certificate>()
+                {
+                    cert
+                }
+            };
+
+            var client = new MongoClient(settings);
+            
+            // just doing a quick read to verify the usability of this connection
+            var database = client.GetDatabase("testDB");
+            var collection = database.GetCollection<BsonDocument>("testCol");
+            
+            var docCount = collection.CountDocuments("{}");
+            Console.WriteLine(docCount);
+        }
+    }
+}
+// end x509 connection