public sealed class ServiceConnectionProperties : Connector 

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.
        }
    });

}

Layer selectedLayer = MapView.Active.GetSelectedLayers()[0];

if (selectedLayer is FeatureLayer)
{
    FeatureLayer featureLayer = selectedLayer as FeatureLayer;

    using (Table table = featureLayer.GetTable())
    using (Datastore datastore = table.GetDatastore())
    {
        ServiceConnectionProperties serviceConnectionProperties = datastore.GetConnector() as ServiceConnectionProperties;

        if (serviceConnectionProperties == null)
            return;

        Uri url = serviceConnectionProperties.URL;      // Will be the URL to the Feature Service.
        string user = serviceConnectionProperties.User;     // The username property will only be
                                                                                                                // populated for feature service hosted
                                                                                                                // on non-federated ArcGIS Server.
        string password = serviceConnectionProperties.Password; // Will always be empty.
    }
}