MongoClient _client;
IMongoDatabase _db;

MongoCredential credential = MongoCredential.CreateMongoCRCredential("pethome", "username", "pwd");
            MongoClientSettings settings = new MongoClientSettings
            {
                Credentials = new List<MongoCredential>() {credential},
                Server = new MongoServerAddress("ip")
            };
            _client = new MongoClient(settings);
            _db = _client.GetDatabase("pethome");