$$USER_ROLES is a new system variable available to users within an aggregation pipeline. It allows them to set what data users are able to access/transform based on their database roles. More details are included in the scope and PD.

Description of Linked Ticket

This ticket encapsulates the work necessary to create a new $$USER_ROLES variable that will be available for find queries and aggregation pipelines. It will be populated at query execution time with the roles of the user executing the query.

On sharded clusters, a query may be executed on a shard by another server node on behalf of the end client. In those cases, $$USER_ROLES will be populated with the roles of the end client's user that the server node is impersonating.