neutron/doc/source/admin/archives/auth.rst

Authentication and authorization

Networking uses the Identity service as the default authentication service. When the Identity service is enabled, users who submit requests to the Networking service must provide an authentication token in X-Auth-Token request header. Users obtain this token by authenticating with the Identity service endpoint. For more information about authentication with the Identity service, see OpenStack Identity service API v3 Reference. When the Identity service is enabled, it is not mandatory to specify the project ID for resources in create requests because the project ID is derived from the authentication token.

The default authorization settings only allow administrative users to create resources on behalf of a different project. Networking uses information received from Identity to authorize user requests. Networking handles two kind of authorization policies:

• Operation-based policies specify access criteria for specific operations, possibly with fine-grained control over specific attributes.
• Resource-based policies specify whether access to specific resource is granted or not according to the permissions configured for the resource (currently available only for the network resource). The actual authorization policies enforced in Networking might vary from deployment to deployment.

The policy engine reads entries from the policy.yaml file. The actual location of this file might vary from distribution to distribution. Entries can be updated while the system is running, and no service restart is required. Every time the policy file is updated, the policies are automatically reloaded. Currently the only way of updating such policies is to edit the policy file. In this section, the terms policy and rule refer to objects that are specified in the same way in the policy file. There are no syntax differences between a rule and a policy. A policy is something that is matched directly from the Networking policy engine. A rule is an element in a policy, which is evaluated. For instance in "create_subnet": "rule:admin_or_network_owner", create_subnet is a policy, and admin_or_network_owner is a rule.

Policies are triggered by the Networking policy engine whenever one of them matches a Networking API operation or a specific attribute being used in a given operation. For instance the create_subnet policy is triggered every time a POST /v2.0/subnets request is sent to the Networking server; on the other hand create_network:shared is triggered every time the shared attribute is explicitly specified (and set to a value different from its default) in a POST /v2.0/networks request. It is also worth mentioning that policies can also be related to specific API extensions; for instance extension:provider_network:set is triggered if the attributes defined by the Provider Network extensions are specified in an API request.

An authorization policy can be composed by one or more rules. If more rules are specified then the evaluation policy succeeds if any of the rules evaluates successfully; if an API operation matches multiple policies, then all the policies must evaluate successfully. Also, authorization rules are recursive. Once a rule is matched, the rule(s) can be resolved to another rule, until a terminal rule is reached.

The Networking policy engine currently defines the following kinds of terminal rules:

• Role-based rules evaluate successfully if the user who submits the request has the specified role. For instance "role:admin" is successful if the user who submits the request is an administrator.
• Field-based rules evaluate successfully if a field of the resource specified in the current request matches a specific value. For instance "field:networks:shared=True" is successful if the shared attribute of the network resource is set to true.
• Generic rules compare an attribute in the resource with an attribute extracted from the user's security credentials and evaluates successfully if the comparison is successful. For instance "tenant_id:%(tenant_id)s" is successful if the project identifier in the resource is equal to the project identifier of the user submitting the request.

This extract is from the default policy.yaml file:

• A rule that evaluates successfully if the current user is an administrator or the owner of the resource specified in the request (project identifier is equal).

  "admin_or_owner": "role:admin or tenant_id:%(tenant_id)s"
  "admin_or_network_owner": "role:admin or tenant_id:%(network_tenant_id)s"
  "admin_only": "role:admin"
  "regular_user": ""
  "shared": "field:networks:shared=True"

• The default policy that is always evaluated if an API operation does not match any of the policies in policy.yaml.

  "default": "rule:admin_or_owner"
  "create_subnet": "rule:admin_or_network_owner"
  "get_subnet": "rule:admin_or_owner or rule:shared"
  "update_subnet": "rule:admin_or_network_owner"
  "delete_subnet": "rule:admin_or_network_owner"
  "create_network": ""

• This policy evaluates successfully if either admin_or_owner, or shared evaluates successfully.

  "get_network": "rule:admin_or_owner or rule:shared"
  "create_network:shared": "rule:admin_only"

• This policy restricts the ability to manipulate the shared attribute for a network to administrators only.

  "update_network": "rule:admin_or_owner"
  "delete_network": "rule:admin_or_owner"
  "create_port": ""
  "create_port:mac_address": "rule:admin_or_network_owner"
  "create_port:fixed_ips": "rule:admin_or_network_owner"

• This policy restricts the ability to manipulate the mac_address attribute for a port only to administrators and the owner of the network where the port is attached.

  "get_port": "rule:admin_or_owner"
  "update_port": "rule:admin_or_owner"
  "delete_port": "rule:admin_or_owner"

In some cases, some operations are restricted to administrators only. This example shows you how to modify a policy file to permit project to define networks, see their resources, and permit administrative users to perform all other operations:

"admin_or_owner": "role:admin or tenant_id:%(tenant_id)s"
"admin_only": "role:admin"
"regular_user": ""
"default": "rule:admin_only"
"create_subnet": "rule:admin_only"
"get_subnet": "rule:admin_or_owner"
"update_subnet": "rule:admin_only"
"delete_subnet": "rule:admin_only"
"create_network": ""
"get_network": "rule:admin_or_owner"
"create_network:shared": "rule:admin_only"
"update_network": "rule:admin_or_owner"
"delete_network": "rule:admin_or_owner"
"create_port": "rule:admin_only"
"get_port": "rule:admin_or_owner"
"update_port": "rule:admin_only"
"delete_port": "rule:admin_only"