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layout	page_title	sidebar_current	description
intro	Access Control Policies	gettingstarted-acl	Access control policies in Vault control what a user can access.

Access Control Policies (ACLs)

Access control policies in Vault control what a user can access. In the last section, we learned about authentication. This section is about authorization.

Whereas for authentication Vault has multiple options or backends that can be enabled and used, the authorization or policies of Vault are always the same format. All authentication backends must map identities back to the core policies that are configured with Vault.

When initializing Vault, there is always one special policy created that can't be removed: the "root" policy. This policy is a special policy that gives superuser access to everything in Vault. An identity mapped to the root policy can do anything.

Policy Format

Policies in Vault are formatted with HCL. HCL is a human-readable configuration format that is also JSON-compatible, so you can use JSON as well. An example policy is shown below:

path "secret/*" {
  policy = "write"
}

path "secret/foo" {
  policy = "read"
}

The policy format uses a prefix matching system on the API path to determine access control. The most specific defined policy is used, either an exact match or the longest-prefix glob match. Since everything in Vault must be accessed via the API, this gives strict control over every aspect of Vault, including mounting backends, authenticating, as well as secret access.

In the policy above, a user could write any secret to secret/, except to secret/foo, where only read access is allowed. Policies default to deny, so any access to an unspecified path is not allowed. The policy langauge changed slightly in Vault 0.2, see this page for details.

Save the above policy as acl.hcl.

Writing the Policy

To write a policy, use the vault policy-write command:

$ vault policy-write secret acl.hcl
Policy 'secret' written.

You can see the policies that are available with vault policies, and you can see the contents of a policy with vault policies <name>. Only users with root access can do this.

Testing the Policy

To use the policy, let's create a token and assign it to that policy. Make sure to save your root token somewhere so you can authenticate back to a root user later.

$ vault token-create -policy="secret"
d97ef000-48cf-45d9-1907-3ea6ce298a29

$ vault auth d97ef000-48cf-45d9-1907-3ea6ce298a29
Successfully authenticated! The policies that are associated
with this token are listed below:

secret

You can now verify that you can write data to secret/, but only read from secret/foo:

$ vault write secret/bar value=yes
Success! Data written to: secret/bar

$ vault write secret/foo value=yes
Error writing data to secret/foo: Error making API request.

URL: PUT http://127.0.0.1:8200/v1/secret/foo
Code: 400. Errors:

* permission denied

You also don't have access to sys according to the policy, so commands such as vault mounts will not work either.

Mapping Policies to Auth Backends

Vault is the single policy authority, unlike auth where you can mount multiple backends. Any mounted auth backend must map identities to these core policies.

Use the vault path-help system with your auth backend to determine how the mapping is done, since it is specific to each backend. For example, with GitHub, it is done by team using the map/teams/<team> path:

$ vault write auth/github/map/teams/default value=secret
Success! Data written to: auth/github/map/teams/default

For GitHub, the "default" team is the default policy set that everyone is assigned to no matter what team they're on.

Other auth backends use alternate, but likely similar mechanisms for mapping policies to identity.

Policies are an important part of Vault. While using the root token is easiest to get up and running, you'll want to restrict access to Vault very quickly, and the policy system is the way to do this.

The syntax and function of policies is easy to understand and work with, and because auth backends all must map to the central policy system, you only have to learn this policy system.

Next, we'll cover how to deploy Vault.

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