public ServiceConnectionProperties( 
   Uri serviceURL
)

{
  //Url examples for (federated) feature services
  //(by "ref" online):
  var url =
      @"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
    }
  });
}

{
  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";

    //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
    //Note: Needs QueuedTask to run
    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 lc = new LayerCreationParams(new Uri(serviceUrl));
    //Note: Needs QueuedTask to run
    LayerFactory.Instance.CreateLayer<MapImageLayer>(lc, map);
}