public ArcGISPortal GetPortal( 
   Uri portalUri
)

var projectPortal = ArcGISPortalManager.Current.GetPortal(new Uri(@"https://<serverName>.<domain>.com/portal/", UriKind.Absolute));
string owner = string.Empty;
await QueuedTask.Run(() => {
  //Get the signed on user name
  owner = projectPortal.GetSignOnUsername();
});
//Get the user content from the portal
var userContent = await projectPortal.GetUserContentAsync(owner);
//Get the first portal project item
var firstPortalProject = userContent.PortalItems.FirstOrDefault(pi => pi.PortalItemType == PortalItemType.ProProject);
var portalProjectUri = firstPortalProject.ItemUri.ToString();
//Check if project can be opened
string docVer = string.Empty;
if (Project.CanOpen(portalProjectUri, out docVer))
{
  await Project.OpenAsync(portalProjectUri);
}
//Note: If Project.CanOpen returns false, the project cannot be opened. One reason could be 
// the active portal is not the same as the portal of the project. Refer to the snippet: [Workflow to open an ArcGIS Pro project](ProSnippets-sharing#workflow-to-open-an-arcgis-pro-project)

//Find the portal to sign in with using its Uri...
var portal = ArcGISPortalManager.Current.GetPortal(new Uri(uri, UriKind.Absolute));
if (!portal.IsSignedOn())
{
  //Calling "SignIn" will trigger the OAuth popup if your credentials are
  //not cached (eg from a previous sign in in the session)
  if (portal.SignIn().success)
  {
    //Set this portal as my active portal
    ArcGISPortalManager.Current.SetActivePortal(portal);
  }
}

var portal = ArcGISPortalManager.Current.GetPortal(new Uri(portalUri));
var portalInfo = await portal.GetPortalInfoAsync();
var orgid = portalInfo.OrganizationId;