We're looking at using Barbican to implement a feature in Heat[1] and
ran into some questions about how secrets are identified in the client.
With most openstack clients, resources are identified by a UUID. You
pass the UUID on the command line (or via the Python API or whatever)
and the client combines that with the endpoint of the service obtained
from the service catalog and a path to the resource type to generate the
URL used to access the resource.
While there appears to be no technical reason that barbicanclient
couldn't also do this, instead of just the UUID it uses the full URL as
the identifier for the resource. This is extremely cumbersome for the
user, and invites confused-deputy attacks where if the attacker can
control the URL, they can get barbicanclient to send a token to an
arbitrary URL. What is the rationale for doing it this way?
In a tangentially related question, since secrets are immutable once
they've been uploaded, what's the best way to handle a case where you
need to rotate a secret without causing a temporary condition where
there is no version of the secret available? (The fact that there's no
way to do this for Nova keypairs is a perpetual problem for people, and
I'd anticipate similar use cases for Barbican.) I'm going to guess it's:
* Create a new secret with the same name
* GET /v1/secrets/?name=<name>&sort=created:desc&limit=1 to find out the
URL for the newest secret with that name
* Use that URL when accessing the secret
* Once the new secret is created, delete the old one
Should this, or whatever the actual recommended way of doing it is, be
baked in to the client somehow so that not every user needs to
reimplement it?
Bottom line: how should Heat expect/require a user to refer to a
Barbican secret in a property of a Heat resource, given that:
- We don't want Heat to become the deputy in "confused deputy attack".
- We shouldn't do things radically differently to the way Barbican does
them, because users will need to interact with Barbican first to store
the secret.
- Many services will likely end up implementing integration with
Barbican and we'd like them all to have similar user interfaces.
- Users will need to rotate credentials without downtime.
cheers,
Zane.
BTW the user documentation for Barbican is really hard to find. Y'all
might want to look in to cross-linking all of the docs you have
together. e.g. there is no link from the Barbican docs to the
python-barbicanclient docs or vice-versa.
[1] https://storyboard.openstack.org/#!/story/2002126
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