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=====
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.

.. code:: ini

  # 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_type = 'keystone_token'
  token = '5b4de0bb77064f289f7cc58e33bea8c7'
  project_id = 'a1e19934af81420d980a5d02b4afe9fb'

  # keystone password credential
  [key_manager]
  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.

.. code:: python

  from castellan.common import utils

  CONF = <your_configuration>
  context = utils.credential_factory(conf=CONF, context=None)

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**

.. code:: python

    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.**

.. code:: python

    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.**

.. code:: python

    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.**

.. code:: python

    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.**

.. code:: python

    from castellan import key_manager

    manager = key_manager.API()

**Example. Using a predetermined configuration object.**

.. code:: python

    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.**

.. code:: python

    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.**

.. code:: python

    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.**

.. code:: python

    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:

.. code:: console

    $ 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.**

.. code:: python

    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
:file:`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.**

.. code:: ini

    [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`:

.. code:: ini

    [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