Attribute-based access control (ABAC) is one of several methods of access control. ABAC defines an access control policy in terms of a user’s organic attributes (such as users who are Federal employees, who are managers and above, who are in agency X or Y).
Systems must know these attributes in order to implement ABAC. When a user accesses a system within their own organization, the system can retrieve the attributes from the local source. But when the user from one organization is accessing a system from another organization, there must be mechanism for these attributes to be conveyed – or exchanged – in a trusted manner.
If you want more information, these sources might be helpful: