Vault Policies

Vault use policies to govern the behavior of clients and instrument Role-Based Access Control (RBAC) by specifying access privileges (authorization).

Vault creates a root policy during initialization. The root policy is capable of performing every operation for all paths. This policy is assigned to the root token that displays when initialization completes. This provides an initial superuser to enable secrets engines, define policies, and configure authentication methods.

Vault also creates a default, policy. The default policy defines a common set of capabilities that enable a token the ability to reflect and manage itself. This policy is also assigned to the root token.

A policy defines a list of paths. Each path expresses the capabilites that are allowed. Capabilities for a path must be granted, as Vault defaults to denying capabilities to paths to ensure that it is secure by default.

»HashiCorp Configuration Language (HCL)

Policies written in HCL format are often referred as ACL Policies. (NOTE: HCL is JSON compatible; therefore JSON can be used as completely valid input.) Sentinel is another framework for policy which is available in Vault Enterprise. Since Sentinel is an enterprise-only feature, this tutorial focuses on writing ACL policies as a foundation.

»Challenge

Since Vault centrally secures, stores, and controls access to secrets across distributed infrastructure and applications, it is critical to control permissions before any user or machine can gain access.

»Solution

Restrict the use of root policy, and write fine-grained policies to practice least privileged. For example, if an app gets AWS credentials from Vault, write policy grants to read from AWS secrets engine but not to delete, etc.

Policies are attached to tokens and roles to enforce client permissions on Vault.

»Prerequisites

To perform the tasks described in this tutorial, you need to have a Vault environment. Refer to the Getting Started tutorial to install Vault. Make sure that your Vault server has been initialized and unsealed.

NOTE: An interactive tutorial is also available if you do not have an environment to perform the steps described in this tutorial. Click the Show Terminal button to start.

»Start Vault in Dev Mode

To experiment with Vault policies, start a Vault server in development mode with root as the root token name.

$ vault server -dev -dev-root-token-id=root

The Vault dev server defaults to running at 127.0.0.1:8200. The server is also initialized and unsealed.

Export an environment variable for the vault CLI to address the Vault server.

$ export VAULT_ADDR=http://127.0.0.1:8200

Export an environment variable for the vault CLI to authenticate with the Vault server.

$ export VAULT_TOKEN=root

The Vault server is ready.

»Write a policy

The first step to create gather policy requirements.

An admin user must be able to:

• Read system health check
• Create and manage ACL policies broadly across Vault
• Enable and manage authentication methods broadly across Vault
• Manage the Key-Value secrets engine enabled at secret/ path

Define the admin policy in the file named admin-policy.hcl.

$ tee admin-policy.hcl <<EOF
# Read system health check
path "sys/health"
{
  capabilities = ["read", "sudo"]
}

# Create and manage ACL policies broadly across Vault

# List existing policies
path "sys/policies/acl"
{
  capabilities = ["list"]
}

# Create and manage ACL policies
path "sys/policies/acl/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# Enable and manage authentication methods broadly across Vault

# Manage auth methods broadly across Vault
path "auth/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# Create, update, and delete auth methods
path "sys/auth/*"
{
  capabilities = ["create", "update", "delete", "sudo"]
}

# List auth methods
path "sys/auth"
{
  capabilities = ["read"]
}

# Enable and manage the key/value secrets engine at `secret/` path

# List, create, update, and delete key/value secrets
path "secret/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# Manage secrets engines
path "sys/mounts/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# List existing secrets engines.
path "sys/mounts"
{
  capabilities = ["read"]
}
EOF

A policy define one or more paths and a list of permitted capabilities. Most of these capabilities map to the HTTP verbs supported by the Vault API.

The sudo capability allows access to paths that are root-protected (Refer to the Root protected endpoints section).

The deny capability disables access to the path. When combined with other capabilities it always precedence.

»Create a policy

Create an admin policy

$ vault policy write admin admin-policy.hcl
Success! Uploaded policy: admin

»Display a policy

$ vault policy list

$ vault policy read admin

»Check token capabilties

A token is able to display its capabilities for a path. This provides a way to verify the capabilities granted or denying by all of its attached policies.

$ ADMIN_TOKEN=$(vault token create -format=json -policy="admin" | jq -r ".auth.client_token")

$ echo $ADMIN_TOKEN
s.MdNlboI0nff3Xpo97d1TfIxd

$ vault token capabilities $ADMIN_TOKEN sys/auth/approle
create, delete, read, sudo, update

$ vault token capabilities $ADMIN_TOKEN identity/entity
deny

»Root protected API endpoints

The following paths requires a root token or sudo capability in the policy:

»Help and Reference

• Policies documentation
• Policy API documentation