public CIMProjectServerConnection ServerConnection {get; set;}

//This workflow would work for 
      var agsFilePath = @"C:\Data\ServerConnectionFiles\AcmeSampleService.ags";

      //ServerConnectionProjectItem supports .ags, .wms, .wmts, .wfs, and .wcs files
      var server_conn_item = ItemFactory.Instance.Create(agsFilePath) 
  as ArcGIS.Desktop.Catalog.ServerConnectionProjectItem;
      
      //Get the server connection - passwords are never returned
      var serverConnection = server_conn_item.ServerConnection as CIMProjectServerConnection;

//Add to an AGS service connection
var service_connection = new CIMAGSServiceConnection()
{
  URL = "URL to the AGS _service_ on the AGS _server_",
  ServerConnection = serverConnection
};

      // Add a new layer to the map
      var layerParams = new LayerCreationParams(service_connection);
      layerParams.MapMemberPosition = MapMemberPosition.AddToBottom;
      var map = MapView.Active.Map;
      await QueuedTask.Run(() =>
      {
          var layer = LayerFactory.Instance.CreateLayer<FeatureLayer>(layerParams, map);
      });