Two aggregation stages:
$listLocalSessions - Ennumerate sessions in the node's LogicalSessionsCache
$listSessions - Ennumerate sessions recorded in the admin.system.sessions collection

Each stage accepts the following spec:
{
allUsers: true|false,
users: [

, ... ],
}

allUsers == true will ennumerate all users from the specified source and requires ActionType::listSessions. Specifying a list of users with allUsers==true is an error.

allUsers == false with no users explicitly specified will default to the currently authenticated user (or non-user if auth is not enabled). If any user is specified in the users array who is NOT the currently logged in user, then ActionType::listSessions is required.