Guide

Policies in Vault

Mar 05, 2018

In this guide, you'll learn how to use policies in Vault, which control access privileges and authorization.

UPDATE: This guide from 2018 may have some outdated information. We recommend you first start with this continuously updated guide to Vault policies on HashiCorp Learn: Vault Policies


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

When you first initialize Vault, the root policy gets created by default. The root policy is a special policy that gives superuser access to everything in Vault. This allows the superuser to set up initial policies, tokens, etc.

In addition, there is another built-in policy,default gets created. The default policy is attached to all tokens and provides common permissions.

Everything in Vault is path based, and admins write policies to grant or forbid access to certain paths and operations in Vault. Vault operates on a secure by default standard, and as such as empty policy grants no permission in the system.

HashiCorp configuration language

Policies written in HCL format are often referred as ACL Policies. Sentinel is another framework for policy which is available in Vault Enterprise. Since Sentinel is an enterprise-only feature, this guide focuses on writing ACL policies as a foundation.

NOTE: HCL is JSON compatible; therefore, JSON can be used as completely valid input.

Reference Material

Estimated time to completion

10 minutes

Personas

The scenario described in this guide introduces the following personas:

  • root sets up initial policies for admin
  • admin is empowered with managing a Vault infrastructure for a team or organizations
  • provisioner configures secret backends and creates policies for client apps

Challenge

Since Vault centrally secures, stores, and controls access tp 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 secret backend but not to delete, etc.

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

Prerequisities

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

» Policy Requirements

Since this guide demonstrates the creation of an admin policy, log in with root token if possible. Otherwise, make sure that you have the following permissions:

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

# List, create, update, and delete auth backends
path "sys/auth/*"
{
  capabilities = ["create", "read", "update", "delete", "sudo"]
}

# To list policies - Step 3
path "sys/policy"
{
  capabilities = ["read"]
}

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

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

# Manage and manage secret backends broadly across Vault.
path "sys/mounts/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# Read health checks
path "sys/health"
{
  capabilities = ["read", "sudo"]
}

# To perform Step 4
path "sys/capabilities"
{
  capabilities = ["create", "update"]
}

# To perform Step 4
path "sys/capabilities-self"
{
  capabilities = ["create", "update"]
}

Steps

The basic workflow of creating policies is:

This guide demonstrates basic policy authoring and management tasks.

  1. Write ACL policies in HCL format
  2. Create policies
  3. View existing policies
  4. Check capabilities of a token

» Step 1: Write ACL policies in HCL format

Remember, empty policy grants no permission in the system. Therefore, ACL policies are defined for each path.

path "<PATH>" {
  capabilities = [ "<LIST_OF_CAPABILITIES>" ]
}

Define one or more capabilities on each path to control operations that are permitted.

Capability Associated HTTP verbs
create POST/PUT
read GET
update POST/PUT
delete DELETE
list LIST

» Policy requirements

First step in creating policies is to gather policy requirements.

Example:

admin is a type of user empowered with managing a Vault infrastructure for a team or organizations. Empowered with sudo, the Administrator is focused on configuring and maintaining the health of Vault cluster(s) as well as providing bespoke support to Vault users.

admin must be able to:

  • Mount and manage auth backends broadly across Vault
  • Mount and manage secret backends broadly across Vault
  • Create and manage ACL policies broadly across Vault
  • Read system health check

provisioner is a type of user or service that will be used by an automated tool (e.g. Terraform) to provision and configure a namespace within a Vault secret backend for a new Vault user to access and write secrets.

provisioner must be able to:

  • Mount and manage auth backends
  • Mount and manage secret backends
  • Create and manage ACL policies

Now, you are ready to author policies to fulfill the requirements.

» Example policy for admin

admin-policy.hcl

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

# List, create, update, and delete auth backends
path "sys/auth/*"
{
  capabilities = ["create", "read", "update", "delete", "sudo"]
}

# List existing policies
path "sys/policy"
{
  capabilities = ["read"]
}

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

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

# Manage and manage secret backends broadly across Vault.
path "sys/mounts/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

# Read health checks
path "sys/health"
{
  capabilities = ["read", "sudo"]
}

» Example policy for provisioner

provisioner-policy.hcl

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

# List, create, update, and delete auth backends
path "sys/auth/*"
{
  capabilities = ["create", "read", "update", "delete", "sudo"]
}

# List existing policies
path "sys/policy"
{
  capabilities = ["read"]
}

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

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

» Step 2: Create policies

Now, create admin and provisioner policies in Vault.

» CLI command

To create policies:

$ vault policy write <POLICY_NAME> <POLICY_FILE>

Example:

# Create admin policy
$ vault policy write admin admin-policy.hcl

# Create provisioner policy
$ vault policy write provisioner provisioner-policy.hcl

NOTE: To update an existing policy, simply re-run the same command by passing your modified policy (*.hcl).

» API call using cURL

To create a policy, use /sys/policy endpoint:

$ curl --header "X-Vault-Token: <TOKEN>" \
       --request PUT \
       --data <PAYLOAD> \
       <VAULT_ADDRESS>/v1/sys/policy/<POLICY_NAME>

Where <TOKEN> is your valid token, and <PAYLOAD> includes policy name and stringfied policy.

Example:

Now, create admin and provisioner policies:

# Create admin policy
$ curl --request PUT --header "X-Vault-Token: ..." --data @admin-payload.json \
    https://vault.rocks/v1/sys/policy/admin

$ cat admin-payload.json
{
  "policy": "path \"auth/*\" { capabilities = [\"create\", \"read\", \"update\", ... }"
}

# Create provisioner policy
$ curl --request PUT --header "X-Vault-Token: ..." --data @provisioner-payload.json \
    https://vault.rocks/v1/sys/policy/provisioner

$ cat provisioner-payload.json
{
  "policy": "path \"auth/*\" { capabilities = [\"create\", \"read\", \"update\", ... }"
}

NOTE: To update an existing policy, simply re-run the same command by passing your modified policy in the request payload (*.json).

» Step 3: View existing policies

Make sure that you see the policies you created in Step 2.

» CLI command

The following command lists existing policies:

$ vault policy list

To view a specific policy:

$ vault policy read <POLICY_NAME>

Example:

# Read admin policy
$ vault policy read admin

# Mount and manage auth backends broadly across Vault
path "auth/*"
{
  capabilities = ["create", "read", "update", "delete", "list", "sudo"]
}

path "sys/auth/*"
{
  capabilities = ["create", "read", "update", "delete", "sudo"]
}

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

» API call using cURL

To list existing ACL policies, use the /sys/policy endpoint.

$ curl --request LIST --header "X-Vault-Token: ..." https://vault.rocks/v1/sys/policy | jq

To read a specific policy, the endpoint path should be /sys/policy/<POLICY_NAME>.

Example:

Read the admin policy:

$ curl --request GET --header "X-Vault-Token: ..." https://vault.rocks/v1/sys/policy/admin | jq
{
  "name": "admin",
  "rules": "# Mount and manage auth backends broadly across Vault\npath \"auth/*\"\n{\n  ...",
  "request_id": "e8151bf3-8136-fef9-428b-1506042350cf",
  "lease_id": "",
  "renewable": false,
  "lease_duration": 0,
  "data": {
  ...

» Step 4: Check capabilities of a token

Use the /sys/capabilities endpoint to fetch the capabilities of a token on a given path. This helps to verify what operations are granted based on the policies attached to the token.

» CLI command

The command is:

$ vault token capabilities <TOKEN> <PATH>

Example:

First, create a token attached to admin policy:

$ vault token create -policy="admin"
Key                Value
---                -----
token              79ecdd41-9bac-1ac7-1ee4-99fbce796221
token_accessor     39b5e8b5-7bbf-6c6d-c536-ba79d3a80dd5
token_duration     768h0m0s
token_renewable    true
token_policies     [admin default]

Now, fetch the capabilities of this token on sys/auth/approle path.

$ vault token capabilities 79ecdd41-9bac-1ac7-1ee4-99fbce796221 sys/auth/approle
Capabilities: [create delete read sudo update]

The result should match the policy rule you wrote on sys/auth/* path. You can repeat the steps to generate a token for provisioner and check its capabilities on paths.

In the absence of token, it returns capabilities of current token invoking this command.

$ vault token capabilities sys/auth/approle
Capabilities: [root]

» API call using cURL

Use the sys/capabilities endpoint.

Example:

First, create a token attached to admin policy:

$ curl --request POST --header "X-Vault-Token: ..." --data '{ "policies":"admin" }' \
       https://vault.rocks/v1/auth/token/create
{
 "request_id": "870ef38c-1401-7beb-633c-ff09cca3db68",
 "lease_id": "",
 "renewable": false,
 "lease_duration": 0,
 "data": null,
 "wrap_info": null,
 "warnings": null,
 "auth": {
   "client_token": "9f3a9fbb-4e1a-87c3-9d4d-ee4d96d40af1",
   "accessor": "f8a269c0-153a-c1ea-ae97-e7e964814392",
   "policies": [
     "root"
   ],
   "metadata": null,
   "lease_duration": 0,
   "renewable": false,
   "entity_id": ""
 }
}

Now, fetch the capabilities of this token on sys/auth/approle path.

# Request payload
$ cat payload.json
{
  "token": "9f3a9fbb-4e1a-87c3-9d4d-ee4d96d40af1",
  "path": "sys/auth/approle"
}

$ curl --request POST --header "X-Vault-Token: ..." --data @payload.json \
    https://vault.rocks/v1/sys/capabilities
{
  "capabilities": [
    "create",
    "delete",
    "read",
    "sudo",
    "update"
  ],
  "request_id": "03f9d5e2-7e8a-4cd3-b9e9-034c058d3d06",
  "lease_id": "",
  "renewable": false,
  "lease_duration": 0,
  "data": {
    "capabilities": [
      "create",
      "delete",
      "read",
      "sudo",
      "update"
    ]
  },
  "wrap_info": null,
  "warnings": null,
  "auth": null
}

The result should match the policy rule you wrote on sys/auth/* path. You can repeat the steps to generate a token for provisioner and check its capabilities on paths.

To check current token's capabilities permitted on a path, use sys/capabilities-self endpoint.

$ curl --request POST --header "X-Vault-Token: ..." --data '{"path":"sys/auth/approle"}' \
    https://vault.rocks/v1/sys/capabilities-self

Next steps

Read the AppRole with Terraform and Chef guide to better understand the role of trusted entities using Terraform and Chef as an example.

To learn more about response wrapping, go to the Cubbyhole Response Wrapping guide.

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