Thanks for posting your question and sorry for the late reply.
In order to request a list of all authenticators using the Management API, the Access Token must contain the read:authentication_methods scope, as mentioned in our Knowledge Article about retrieving all authenticators for a certain user. This endpoint can be used: GET /api/v2/users/{id}/authentication-methods, detailed here.
Leaving this here since it might help others as well.
Thanks,
Remus