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Policies
========

Glance's public API calls may be restricted to certain sets of users using a 
policy configuration file. This document explains exactly how policies are
configured and what they apply to. 

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 the authorized tenant.

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

A policy configuration file is a simply JSON object 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`` - List available image entities
  
  * ``GET /v1/images``
  * ``GET /v1/images/detail``
  * ``GET /v2/images``

* ``get_image`` - Retrieve a specific image entity
  
  * ``HEAD /v1/images/<IMAGE_ID>``
  * ``GET /v1/images/<IMAGE_ID>``
  * ``GET /v2/images/<IMAGE_ID>``

* ``download_image`` - Download binary image data
  
  * ``GET /v1/images/<IMAGE_ID>``
  * ``GET /v2/images/<IMAGE_ID>/file``

* ``add_image`` - Create an image entity
  
  * ``POST /v1/images``
  * ``POST /v2/images``

* ``modify_image`` - Update an image entity

  * ``PUT /v1/images/<IMAGE_ID>``
  * ``PUT /v2/images/<IMAGE_ID>``

* ``publicize_image`` - Create or update images with attribute

  * ``POST /v1/images`` with attribute ``is_public`` = ``true``
  * ``PUT /v1/images/<IMAGE_ID>`` with attribute ``is_public`` = ``true``
  * ``POST /v2/images`` with attribute ``visibility`` = ``public``
  * ``PUT /v2/images/<IMAGE_ID>`` with attribute ``visibility`` = ``public``

* ``delete_image`` - Delete an image entity and associated binary data

  * ``DELETE /v1/images/<IMAGE_ID>``
  * ``DELETE /v2/images/<IMAGE_ID>``

* ``manage_image_cache`` - Allowed to use the image cache management API


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"]
  }
