Identity API protection with role-based access control (RBAC)

Identity API protection with role-based access control (RBAC)

Like most OpenStack projects, Identity supports the protection of its APIs by defining policy rules based on an RBAC approach. Identity stores a reference to a policy JSON file in the main Identity configuration file, /etc/keystone/keystone.conf. Typically this file is named policy.json, and contains the rules for which roles have access to certain actions in defined services.

Each Identity API v3 call has a line in the policy file that dictates which level of governance of access applies.

API_NAME: RULE_STATEMENT or MATCH_STATEMENT

Where:

RULE_STATEMENT can contain RULE_STATEMENT or MATCH_STATEMENT.

MATCH_STATEMENT is a set of identifiers that must match between the token provided by the caller of the API and the parameters or target entities of the API call in question. For example:

"identity:create_user": "role:admin and domain_id:%(user.domain_id)s"

Indicates that to create a user, you must have the admin role in your token. The domain_id in your token must match the domain_id in the user object that you are trying to create, which implies this must be a domain-scoped token. In other words, you must have the admin role on the domain in which you are creating the user, and the token that you use must be scoped to that domain.

Each component of a match statement uses this format:

ATTRIB_FROM_TOKEN:CONSTANT or ATTRIB_RELATED_TO_API_CALL

The Identity service expects these attributes:

Attributes from token:

  • user_id

  • domain_id

  • project_id

The project_id attribute requirement depends on the scope, and the list of roles you have within that scope.

Attributes related to API call:

  • user.domain_id

  • Any parameters passed into the API call

  • Any filters specified in the query string

You reference attributes of objects passed with an object.attribute syntax (such as, user.domain_id). The target objects of an API are also available using a target.object.attribute syntax. For instance:

"identity:delete_user": "role:admin and domain_id:%(target.user.domain_id)s"

would ensure that Identity only deletes the user object in the same domain as the provided token.

Every target object has an id and a name available as target.OBJECT.id and target.OBJECT.name. Identity retrieves other attributes from the database, and the attributes vary between object types. The Identity service filters out some database fields, such as user passwords.

List of object attributes:

role:
     target.role.id
     target.role.name

user:
     target.user.default_project_id
     target.user.description
     target.user.domain_id
     target.user.enabled
     target.user.id
     target.user.name

group:
     target.group.description
     target.group.domain_id
     target.group.id
     target.group.name

domain:
     target.domain.enabled
     target.domain.id
     target.domain.name

project:
     target.project.description
     target.project.domain_id
     target.project.enabled
     target.project.id
     target.project.name

The default policy.json file supplied provides a somewhat basic example of API protection, and does not assume any particular use of domains. Refer to policy.v3cloudsample.json as an example of multi-domain configuration installations where a cloud provider wants to delegate administration of the contents of a domain to a particular admin domain. This example policy file also shows the use of an admin_domain to allow a cloud provider to enable administrators to have wider access across the APIs.

A clean installation could start with the standard policy file, to allow creation of the admin_domain with the first users within it. You could then obtain the domain_id of the admin domain, paste the ID into a modified version of policy.v3cloudsample.json, and then enable it as the main policy file.

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