Within a project I would like to make some maps available to view by the client but not publicly visible.
Allow External Viewers that require Login. This would enable clients and sub-consultants a view of a single map but without making the map publicly available and also not one of the organisation Level 1 viewers.
Similar capabilities are available in SharePoint sites where users who are not part of the organisation can view pages. It would require an ESRI account to be set up for this. Example of how this is done by Microsoft: Share sites or documents with people outside your organization - Office Support