open-vault/website/source/docs/auth/app-id.html.md

---
layout: "docs"
page_title: "Auth Backend: App ID"
sidebar_current: "docs-auth-appid"
description: |-
  The App ID auth backend is a mechanism for machines to authenticate with Vault.
---

# Auth Backend: App ID

Name: `app-id`

The App ID auth backend is a mechanism for machines to authenticate with Vault.
It works by requiring two hard-to-guess unique pieces of information: a unique
app ID, and a unique user ID.

The goal of this credential provider is to allow elastic users (dynamic
machines, containers, etc.) to authenticate with Vault without having to store
passwords outside of Vault. It is a single method of solving the
chicken-and-egg problem of setting up Vault access on a machine.  With this
provider, nobody except the machine itself has access to both pieces of
information necessary to authenticate. For example: configuration management
will have the app IDs, but the machine itself will detect its user ID based on
some unique machine property such as a MAC address (or a hash of it with some
salt).

An example, real world process for using this provider:

  1. Create unique app IDs (UUIDs work well) and map them to policies.  (Path:
     map/app-id/<app-id>)

  2. Store the app IDs within configuration management systems.

  3. An out-of-band process run by security operators map unique user IDs to
     these app IDs. Example: when an instance is launched, a cloud-init system
     tells security operators a unique ID for this machine. This process can be
     scripted, but the key is that it is out-of-band and out of reach of
     configuration management.  (Path: map/user-id/<user-id>)

  4. A new server is provisioned. Configuration management configures the app
     ID, the server itself detects its user ID. With both of these pieces of
     information, Vault can be accessed according to the policy set by the app
     ID.

More details on this process follow:

The app ID is a unique ID that maps to a set of policies. This ID is generated
by an operator and configured into the backend. The ID itself is usually a
UUID, but any hard-to-guess unique value can be used.

After creating app IDs, an operator authorizes a fixed set of user IDs with
each app ID. When a valid {app ID, user ID} tuple is given to the "login" path,
then the user is authenticated with the configured app ID policies.

The user ID can be any value (just like the app ID), however it is generally a
value unique to a machine, such as a MAC address or instance ID, or a value
hashed from these unique values.


## Authentication

#### Via the CLI

Use `vault write`, for example: `vault write auth/app-id/login/[app-id] user_id=[user-id]`

#### Via the API

The endpoint for the App ID login is `auth/app-id/login/[app_id]`. The client is expected
to provide the `user_id` parameter as part of the request.

## Configuration

First you must enable the App ID auth backend:

```
$ vault auth-enable app-id
Successfully enabled 'app-id' at 'app-id'!
```

Now when you run `vault auth -methods`, the App ID backend is available:

```
Path       Type      Description
app-id/    app-id
token/     token     token based credentials
```

To use the App ID auth backend, an operator must configure it with
the set of App IDs, user IDs, and the mapping between them. An
example is shown below, use `vault path-help` for more details.

```
$ vault write auth/app-id/map/app-id/foo value=root display_name=foo
...

$ vault write auth/app-id/map/user-id/bar value=foo cidr_block=10.0.0.0/16
...
```

The above creates an App ID "foo" that associates with the policy "root".
The `display_name` sets the display name for audit logs and secrets.
Next, we configure the user ID "bar" and say that the user ID bar
can be paired with "foo" but only if the client is in the "10.0.0.0/16" CIDR block.
The `cidr_block` configuration is optional.

This means that if a client authenticates and provide both "foo" and "bar",
then the app ID will authenticate that client with the policy "root".

In practice, both the user and app ID are likely hard-to-guess UUID-like values.

Note that it is possible to authorize multiple app IDs with each
user ID by writing them as comma-separated values to the user ID mapping:

```
$ vault write auth/app-id/map/user-id/bar value=foo,baz cidr_block=10.0.0.0/16
...
```