How can I query users created in $external database

I'm trying to configure certificate based mongo authentication, generally it works fine but there's one question I cannot find answer for. Suppose I created a user in $external database:

use $external
db.createUser({user: "emailAddress=jsmith@example.com,CN=jsmith,OU=Mongo Admins,O=Initech,C=US",
               roles: [{"role" : "root","db" : "admin"}]
})

Q: How can I query the content of $external database, particularly users data?

Is there any similar way to:

use admin
db.system.users.find()