It might happen that you, as owner, want several people accessing the Drupal cluster in order to manage your site(s). To do this, go to https://application-portal.web.cern.ch/, search for your application in the form of webframeworks-drupal-{PROJECT}.
Under the Application details, click on 
and a new window will pop up.
In this new window, under Administrator Group, we click on 
and we look for the corresponding group:
Finally we click on 
and the selected group will appear as Administrators:
As of this moment onwards, people belonging to the aforementioned group will have access to the https://drupal.cern.ch cluster, and will be able to manage your Drupal site(s) with administrator permissions.