You can specify your ArcGIS organization's subdomain to enable enterprise logins across your SharePoint site collection. Configuring enterprise logins allows members of your organization to sign in to ArcGIS for SharePoint using the same credentials they use to access your enterprise information systems. The advantage of setting up enterprise logins is that members do not need to create additional logins within ArcGIS; instead, they can use the account that is already set up within their enterprise system.
To configure enterprise logins, type the subdomain of your ArcGIS Online organization in the URL field on the app's configuration page. For detailed instructions, see Configure ArcGIS for SharePoint.