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Policies
========

Glance's API calls may be restricted to certain sets of users using
a Policy configuration file.

This document explains exactly how policies work and how the policy
configuration file is constructed.

Basics
------

A policy is composed of a set of rules that are used by the Policy "Brain"
in determining if a particular action may be performed by a particular
role.

Constructing a Policy Configuration File
----------------------------------------

Policy configuration files are simply serialized JSON dictionaries that
contain sets of rules. Each top-level key is the name of a rule. Each rule
is a string that describes an action that may be performed in the Glance API.

The actions that may have a rule enforced on them are:

* ``get_images`` - Allowed to call the ``GET /images`` and
  ``GET /images/detail`` API calls

* ``get_image`` - Allowed to call the ``HEAD /images/<IMAGE_ID>`` and
  ``GET /images/<IMAGE_ID>`` API calls

* ``add_image`` - Allowed to call the ``POST /images`` API call

* ``modify_image`` - Allowed to call the ``PUT /images/<IMAGE_ID>`` API call

* ``delete_image`` - Allowed to call the ``DELETE /images/<IMAGE_ID>`` API call

To limit an action to a particular role or roles, you list the roles like so ::

  {
    "delete_image": ["role:admin", "role:superuser"]
  }

The above would add a rule that only allowed users that had roles of either
"admin" or "superuser" to delete an image.

Examples
--------

Example 1. (The default policy configuration)

 ::

  {
      "default": []
  }

Note that an empty JSON list means that all methods of the
Glance API are callable by anyone.

Example 2. Disallow modification calls to non-admins

 ::

  {
      "default": [],
      "add_image": ["role:admin"],
      "modify_image": ["role:admin"],
      "delete_image": ["role:admin"]
  }