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---
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layout: "docs"
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page_title: "Auth Backend: App ID"
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sidebar_current: "docs-auth-appid"
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description: |-
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The App ID auth backend is a mechanism for machines to authenticate with Vault.
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---
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# Auth Backend: App ID
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Name: `app-id`
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The App ID auth backend is a mechanism for machines to authenticate with
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Vault. It works by requiring two hard-to-guess unique pieces of information:
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a unique app ID, and a unique user ID.
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The goal of this credential provider is to allow elastic users
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(dynamic machines, containers, etc.) to authenticate with Vault without
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having to store passwords outside of Vault. It is a single method of
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solving the chicken-and-egg problem of setting up Vault access on a machine.
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With this provider, nobody except the machine itself has access to both
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pieces of information necessary to authenticate. For example:
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configuration management will have the app IDs, but the machine itself
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will detect its user ID based on some unique machine property such as a
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MAC address (or a hash of it with some salt).
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An example, real world process for using this provider:
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1. Create unique app IDs (UUIDs work well) and map them to policies.
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(Path: map/app-id/<app-id>)
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2. Store the app IDs within configuration management systems.
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3. An out-of-band process run by security operators map unique user IDs
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to these app IDs. Example: when an instance is launched, a cloud-init
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system tells security operators a unique ID for this machine. This
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process can be scripted, but the key is that it is out-of-band and
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out of reach of configuration management.
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(Path: map/user-id/<user-id>)
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4. A new server is provisioned. Configuration management configures the
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app ID, the server itself detects its user ID. With both of these
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pieces of information, Vault can be accessed according to the policy
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set by the app ID.
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More details on this process follow:
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The app ID is a unique ID that maps to a set of policies. This ID is
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generated by an operator and configured into the backend. The ID itself
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is usually a UUID, but any hard-to-guess unique value can be used.
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After creating app IDs, an operator authorizes a fixed set of user IDs
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2015-04-29 05:04:58 +00:00
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with each app ID. When a valid {app ID, user ID} tuple is given to the
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"login" path, then the user is authenticated with the configured app
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ID policies.
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The user ID can be any value (just like the app ID), however it is
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generally a value unique to a machine, such as a MAC address or instance ID,
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or a value hashed from these unique values.
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## Authentication
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#### Via the CLI
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App ID authentication is not allowed via the CLI.
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#### Via the API
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2015-05-15 18:32:48 +00:00
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The endpoint for the App ID login is `/login`. The client is expected
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to provide the `app_id` and `user_id` parameters as part of the request.
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## Configuration
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2015-05-07 17:41:23 +00:00
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First you must enable the App ID auth backend:
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```
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$ vault auth-enable app-id
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Successfully enabled 'app-id' at 'app-id'!
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```
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Now when you run `vault auth -methods`, the App ID backend is available:
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```
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Path Type Description
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app-id/ app-id
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token/ token token based credentials
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```
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To use the App ID auth backend, an operator must configure it with
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the set of App IDs, user IDs, and the mapping between them. An
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example is shown below, use `vault help` for more details.
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```
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$ vault write auth/app-id/map/app-id/foo value=root display_name=foo
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...
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$ vault write auth/app-id/map/user-id/bar value=foo cidr_block=10.0.0.0/16
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...
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```
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The above creates an App ID "foo" that associates with the policy "root".
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The `display_name` sets the display name for audit logs and secrets.
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Next, we configure the user ID "bar" and say that the user ID bar
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can be paired with "foo" but only in client is in the "10.0.0.0/16" CIDR block.
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The `cidr_block` configuration is optional.
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This means that if a client authenticates and provide both "foo" and "bar",
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then the app ID will authenticate that client with the policy "root".
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In practice, both the user and app ID are likely hard-to-guess UUID-like values.
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