---
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 the valid {app ID, user ID} set is 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

App ID authentication is not allowed via the CLI.

#### Via the API

The endpoint for the App ID login is `/login`.

## Configuration

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 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 in 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.
