Here is with username and password

var localHostElasticURL= "http://localhost:9200";
  string indexFormat = "stackOverFlowTestindex";
  Log.Logger = new LoggerConfiguration()
      .Enrich.FromLogContext()
      .Enrich.WithExceptionDetails()
      .Enrich.WithProperty("Environment", environment)
      .WriteTo.Elasticsearch(new[] { new Uri(localHostElasticURL) },
      options =>
      {
          options.DataStream = new DataStreamName(indexFormat);
          options.TextFormatting = new EcsTextFormatterConfiguration();
          options.BootstrapMethod = BootstrapMethod.Failure;
          options.ConfigureChannel = channelOptions =>
          {
              channelOptions.BufferOptions = new BufferOptions();
          };
      },
      configureTransport =>
      {
            configureTransport.Authentication(new BasicAuthentication("username", "password"));
            configureTransport.ServerCertificateValidationCallback((_, _, _, _) => true);
      })
      .ReadFrom.Configuration(configuration)
      .CreateLogger();

  host.UseSerilog(Log.Logger, true);

but anyone can help with indexFormat like be-logs-{0:yyyy.MM} to always create new index each month and have alias like be-logs.