Usage

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),
                              tenant=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.

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

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