public ServiceConnectionProperties( 
   Uri serviceURL
)

public async Task OpenFeatureServiceUsingUrl(string url)
{
    //Url examples for (federated) feature services
    //(by "ref" online):
    //https://sampleserver6.arcgisonline.com/arcgis/rest/services/LocalGovernment/Recreation/FeatureServer
    //(federated by ref on portal)
    //https://portal.example.com/server/rest/services/FeatureServiceName/FeatureServer");
    //(federated by value - Hosted - on portal)
    //https://portal.example.com/server/rest/services/Hosted/FeatureServiceName/FeatureServer");

    await QueuedTask.Run(() =>
    {
        var uri = new Uri(url, UriKind.Absolute);
        using (var fs_db = new ArcGIS.Core.Data.Geodatabase(new ServiceConnectionProperties(uri)))
        {
            //Use the geodatabase
        }
    });
}

public async void ConnectToDifferentTypesOfFeatureService()
{
    await QueuedTask.Run(() =>
    {
        Uri nonFederatedServerURL = new Uri(
        "https://arcgis.server.example.com:6443/arcgis/rest/services/FeatureServiceName/FeatureServer");

        // Note that for non-federated ArcGIS Server hosted feature services,
        // the username and password have to be specified always.
        ServiceConnectionProperties nonFederatedArcGISServer =
                    new ServiceConnectionProperties(nonFederatedServerURL)
                    {
                        User = "serverUser",
                        Password = "serverPassword"
                    };

        using (Geodatabase nonFederatedServerFeatureService =
            new Geodatabase(nonFederatedArcGISServer))
        {
            // Use the feature service geodatabase.
        }

        //Hosted (or published "by value")
        Uri federatedServerURL = new Uri(
            "http://federated.with.portal.example.com/server/rest/services/Hosted/FeatureServiceName/FeatureServer");
        //Published "by reference"
        //Uri federatedServerURL = new Uri(
        //"http://federated.with.portal.example.com/server/rest/services/FeatureServiceName/FeatureServer");

        // Note that for feature services hosted on ArcGIS Server federated with
        // ArcGIS Portal, the username and password cannot be specified through the API. 
        // Even if the username and password were specified, they will be disregarded.
        // Instead the Portal authorization has to be configured by adding the Portal to
        // ArcGIS Pro with the user with which the connection should be established.
        // To connect to a Portal from a CoreHost application, use the
        // ArcGIS.Core.SystemCore.ArcGISSignOn class to authenticate with the Portal.

        ServiceConnectionProperties federatedArcGISServer =
            new ServiceConnectionProperties(federatedServerURL);

        using (Geodatabase federatedServerFeatureService =
            new Geodatabase(federatedArcGISServer))
        {
            // Use the feature service geodatabase.
        }

        Uri arcgisOnlineURL = new Uri(
            "http://services1.arcgis.com/47GG2ga246DGaLwa/arcgis/rest/services/FeatureServiceName/FeatureServer");
        //or
        //https://sampleserver6.arcgisonline.com/arcgis/rest/services/LocalGovernment/Recreation/FeatureServer
        //etc

        // Similar to Federated Feature Services, note that for feature services
        // hosted on ArcGIS Online, the username and password cannot be specified through
        // the API. Even if the username and password were specified, they will be
        // disregarded. Instead the connection will be established based on the ArcGIS
        // Online user credentials used to login to ArcGIS Pro at startup.

        ServiceConnectionProperties arcGISOnline =
            new ServiceConnectionProperties(arcgisOnlineURL);

        using (Geodatabase arcGISOnlineFeatureService =
            new Geodatabase(arcGISOnline))
        {
            // Use the feature service geodatabase.
        }
    });

}

      //Connect to the AGS service. Note: the connection will persist for the
      //duration of the Pro session.
      var serverUrl = "https://sampleserver6.arcgisonline.com/arcgis/rest/services";

      var username = "user1";
      var password = "user1";

await QueuedTask.Run(() =>
{
  //at any point before creating a layer, first make a connection to the server
  //if one has not been already established for the current session
  var uri = new Uri(serverUrl);
  var props = new ServiceConnectionProperties(uri)
  {
    User = username
  };
  //It is preferred that you use the Windows Credential Manager to store the password

  //However, it can be set as clear text if you so choose
  props.Password = password; //not recommended

          //Establish a connection to the server at any point in time _before_
          //creating a layer from a service on the server
          var gdb = new Geodatabase(props);
  gdb.Dispose();//you do not need the geodatabase object after you have connected.
});

      //later in the session, as needed...create a layer from one of the services
//on the server
      var serviceUrl = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire_secure/MapServer";
var map = MapView.Active.Map;

      QueuedTask.Run(() =>
      {
          var lc = new LayerCreationParams(new Uri(serviceUrl));
          LayerFactory.Instance.CreateLayer<MapImageLayer>(lc, map);
      });