Usage¶
This document describes some of the common usage patterns for Castellan. When incorporating this package into your applications, care should be taken to consider the key manager behavior you wish to encapsulate and the OpenStack deployments on which your application will run.
Authentication¶
A fundamental concept to using Castellan is the credential context object. Castellan supports the following credentials for authentication:
Token
Password
Keystone Token
Keystone Password
In order to use these credentials, valid configuration parameters must be provided.
# token credential
# token variable not required, token can be obtained from context
[key_manager]
auth_type = 'token'
token = '5b4de0bb77064f289f7cc58e33bea8c7'
# password credential
[key_manager]
auth_type = 'password'
username = 'admin'
password = 'passw0rd1'
# keystone token credential
[key_manager]
auth_url = 'http://192.169.5.254:5000'
auth_type = 'keystone_token'
token = '5b4de0bb77064f289f7cc58e33bea8c7'
project_id = 'a1e19934af81420d980a5d02b4afe9fb'
# keystone password credential
[key_manager]
auth_url = 'http://192.169.5.254:5000'
auth_type = 'keystone_password'
username = 'admin'
password = 'passw0rd1'
project_id = '1099302ec608486f9879ba2466c60720'
user_domain_name = 'default'
Note
Keystone Token and Password authentication is achieved using keystoneauth1.identity Token and Password auth plugins. There are a variety of different variables which can be set for the keystone credential options.
The configuration must be passed to a credential factory which will generate the appropriate context.
from castellan.common import utils
CONF = cfg.CONF
CONF(default_config_files=['~/castellan.conf'])
context = utils.credential_factory(conf=CONF)
Now you can go ahead and pass the context and use it for authentication.
Note
There is a special case for a token. Since a user may not want to store a token in the configuration, the user can pass a context object containing an ‘auth_token’ as well as a configuration file with ‘token’ as the auth type.
An oslo context object can also be used for authentication, it is
frequently inherited from oslo.context.RequestContext. This object
represents information that is contained in the current request, and is
usually populated in the WSGI pipeline. The information contained in this
object will be used by Castellan to interact with the specific key manager
that is being abstracted.
Example. Creating RequestContext from Keystone Client
from keystoneauth1 import identity
from keystoneauth1 import session
from oslo_context import context
username = 'admin'
password = 'openstack'
project_name = 'admin'
auth_url = 'http://localhost/identity/v3'
auth = identity.Password(auth_url=auth_url,
username=username,
password=password,
project_name=project_name,
default_domain_id='default')
sess = session.Session()
ctxt = context.RequestContext(auth_token=auth.get_token(sess),
project_id=auth.get_project_id(sess))
ctxt can then be passed into any key_manager api call.
Basic usage¶
Castellan works on the principle of providing an abstracted key manager based on your configuration. In this manner, several different management services can be supported through a single interface.
In addition to the key manager, Castellan also provides primitives for various types of secrets (for example, asymmetric keys, simple passphrases, and certificates). These primitives are used in conjunction with the key manager to create, store, retrieve, and destroy managed secrets.
Example. Creating and storing a key.
import myapp
from castellan.common.objects import passphrase
from castellan import key_manager
key = passphrase.Passphrase('super_secret_password')
manager = key_manager.API()
stored_key_id = manager.store(myapp.context(), key)
To begin with, we’d like to create a key to manage. We create a simple passphrase key, then instantiate the key manager, and finally store it to the manager service. We record the key identifier for later usage.
Example. Retrieving a key and checking the contents.
import myapp
from castellan import key_manager
manager = key_manager.API()
key = manager.get(myapp.context(), stored_key_id)
if key.get_encoded() == 'super_secret_password':
myapp.do_secret_stuff()
This example demonstrates retrieving a stored key from the key manager service and checking its contents. First we instantiate the key manager, then retrieve the key using a previously stored identifier, and finally we check the validity of key before performing our restricted actions.
Example. Deleting a key.
import myapp
from castellan import key_manager
manager = key_manager.API()
manager.delete(myapp.context(), stored_key_id)
Having finished our work with the key, we can now delete it from the key manager service. We once again instantiate a key manager, then we simply delete the key by using its identifier. Under normal conditions, this call will not return anything but may raise exceptions if there are communication, identification, or authorization issues.
Example. Secret consumers.
import myapp
from castellan import key_manager
manager = key_manager.API()
# Listing consumers:
stored_secret = self.key_mgr.get(myapp.context(), stored_id)
consumer_list = stored_secret.consumers # consumers is a list of dicts
# Adding consumers:
consumer = {'service': 'glance',
'resource_type': 'image',
'resource_id': 'image_id'}
try:
manager.add_consumer(myapp.context(), stored_id, consumer)
except NotImplementedError:
pass # backends like Vault don't support adding/removing consumers
# Remove the consumer before calling secret delete without the force flag:
try:
manager.remove_consumer(myapp.context(), stored_id, consumer)
except NotImplementedError:
pass
manager.delete(myapp.context(), stored_key_id)
# Alternatively, force delete a secret
manager.delete(myapp.context(), stored_key_id, force=True)
After creating a secret, we can add consumers to it. Secrets with consumers cannot be deleted without using the force flag.
Note
Secret consumers are currently only avaliable for the Barbican backend. https://docs.openstack.org/barbican/latest/api/reference/secret_consumers.html
Configuring castellan¶
Castellan contains several options which control the key management
service usage and the configuration of that service. It also contains
functions to help configure the defaults and produce listings for use
with the oslo-config-generator application.
In general, castellan configuration is handled by passing an
oslo_config.cfg.ConfigOpts object into the
castellan.key_manager.API call when creating your key manager. By
default, when no ConfigOpts object is provided, the key manager will
use the global oslo_config.cfg.CONF object.
Example. Using the global CONF object for configuration.
from castellan import key_manager
manager = key_manager.API()
Example. Using a predetermined configuration object.
from oslo_config import cfg
from castellan import key_manager
conf = cfg.ConfigOpts()
manager = key_manager.API(configuration=conf)
Controlling default options¶
To change the default behavior of castellan, and the key management service
it uses, the castellan.options module provides the set_defaults
function. This function can be used at run-time to change the behavior of
the library or the key management service provider.
Example. Changing the barbican endpoint.
from oslo_config import cfg
from castellan import options
from castellan import key_manager
conf = cfg.ConfigOpts()
options.set_defaults(conf, barbican_endpoint='http://192.168.0.1:9311/')
manager = key_manager.API(conf)
Example. Changing the key manager provider while using the global configuration.
from oslo_config import cfg
from castellan import options
from castellan import key_manager
options.set_defaults(cfg.CONF, api_class='some.other.KeyManager')
manager = key_manager.API()
Logging from within Castellan¶
Castellan uses oslo_log for logging. Log information will be generated
if your application has configured the oslo_log module. If your
application does not use oslo_log then you can enable default logging
using enable_logging in the castellan.options module.
Example. Enabling default logging.
from castellan import options
from castellan import key_manager
options.enable_logging()
manager = key_manager.API()
Generating sample configuration files¶
Castellan includes a tox configuration for creating a sample configuration file. This file will contain only the values that will be used by castellan. To produce this file, run the following command from the root of the castellan project directory:
$ tox -e genconfig
Parsing the configuration files¶
Castellan does not parse the configuration files by default. When you create
the files and occupy them, you still need to manipulate the
oslo_config.cfg object before passing it to the
castellan.key_manager.API object. You can create a list of locations where
the configuration files reside. If multiple configuration files are
specified, the variables will be used from the most recently parsed file and
overwrite any previous variables. In the example below, the configuration
file in the /etc/castellan directory will overwrite the values found in
the file in the user’s home directory. If a file is not found in one of the
specified locations, then a config file not found error will occur.
Example. Parsing the config files.
from oslo_config import cfg
from castellan import key_manager
conf=cfg.CONF
config_files = ['~/castellan.conf', '/etc/castellan/castellan.conf']
conf(default_config_files=config_files)
manager = key_manager.API(configuration=conf)
There are two options for parsing the Castellan values from a configuration file:
The values can be placed in a separate file.
You can include the values in a configuration file you already use.
In order to see all of the default values used by Castellan, generate a sample configuration by referring to the section directly above.
Adding castellan to configuration files¶
One common task for OpenStack projects is to create project configuration
files. Castellan provides a list_opts function in the
castellan.options module to aid in generating these files when using
the oslo-config-generator. This function can be specified in the
setup.cfg file of your project to inform oslo of the
configuration options. Note, this will use the default values supplied
by the castellan package.
Example. Adding castellan to the oslo.config entry point.
[entry_points]
oslo.config.opts =
castellan.config = castellan.options:list_opts
The new namespace also needs to be added to your project’s oslo-config-generator conf, e.g. etc/oslo-config-generator/myproject.conf:
[DEFAULT]
output_file = etc/myproject/myproject.conf
namespace = castellan.config
For more information on the oslo configuration generator, please see https://docs.openstack.org/oslo.config/latest/cli/generator.html
