set auth alias custom metadata to service account annotations

[thyton]

Overview

This PR sets auth alias custom metadata to service account annotations. Users can create policy rules that use custom entity/alias metadata and have this metadata be supplied from Kubernetes annotations on the ServiceAccount.

Design of Change

Extra permission configuration for installations is required to allow to get annotations from Kubernetes. A new use_annotations_as_alias_metadata config option is added for users to explicitly opt-in to ensure existing installations still work if this option is opted out.

Only annotations with the prefix vault.hashicorp.com/alias-metadata- of the client token's associated service account will be added to the auth alias's metadata upon a login request. For example, if an annotation "vault.hashicorp.com/alias-metadata-foo" is configured, "foo" with its value will be added.

NOTE that Vault will need permission to read service accounts from the Kubernetes API.

Example:

# Service Account "default" in "default" namespace
kubectl get serviceaccount default -n default -o json
{
    "apiVersion": "v1",
    "kind": "ServiceAccount",
    "metadata": {
        "annotations": {
            "auth-metadata.vault.hashicorp.com/alias-metadata-bar": "baz",
            "auth-metadata.vault.hashicorp.com/alias-metadata-foo": "bar"
        },
        "creationTimestamp": "2024-01-07T23:27:24Z",
        "name": "default",
        "namespace": "default",
        "resourceVersion": "5514",
        "uid": "ddae5be7-3aaa-4256-adc4-b77ea508e25e"
    }
}

# Configure a role "demo" with bound_service_account_names=default bound_service_account_namespaces=default
vault write auth/kubernetes/role/demo bound_service_account_names=default bound_service_account_namespaces=default policies=default ttl=1h
Success! Data written to: auth/kubernetes/role/demo

# Login request to vault.
vault write auth/kubernetes/login role=demo jwt=$(kubectl create token -n default default)
Key                                       Value
---                                       -----
token                                     hvs.CAESIAD96sjSFtZU6BXo5E1SuPoXcb_M_PJ9CSs0fM4OEcVMGh4KHGh2cy5kdTJid1JUeDRPZ3dXOVYzUTQxS3Zkc1Q
token_accessor                            FNQlfHrY2ioNmsKiX4EqACjJ
token_duration                            1h
token_renewable                           true
token_policies                            ["default"]
identity_policies                         []
policies                                  ["default"]
token_meta_role                           demo
token_meta_service_account_name           default
token_meta_service_account_namespace      default
token_meta_service_account_secret_name    n/a
token_meta_service_account_uid            ddae5be7-3aaa-4256-adc4-b77ea508e25e

# A new entity alias was created
vault list identity/entity-alias/id 
Keys
----
c474b739-f5d7-9b42-a8ea-d192972d832d

# The entity alias is expected to have the customized key value pairs from the SA annotations together with other pairs for vault internal use.
vault read identity/entity-alias/id/c474b739-f5d7-9b42-a8ea-d192972d832d
Key                          Value
---                          -----
canonical_id                 7281fda9-12c3-66aa-43d1-8e9817731d26
creation_time                2024-01-08T00:47:57.77138992Z
custom_metadata              <nil>
id                           c474b739-f5d7-9b42-a8ea-d192972d832d
last_update_time             2024-01-08T00:47:57.77138992Z
local                        false
merged_from_canonical_ids    <nil>
metadata                     map[foo:bar bar:baz service_account_name:default service_account_namespace:default service_account_secret_name: service_account_uid:ddae5be7-3aaa-4256-adc4-b77ea508e25e]
mount_accessor               auth_kubernetes-dev_6c913879
mount_path                   auth/kubernetes/
mount_type                   kubernetes-dev
name                         ddae5be7-3aaa-4256-adc4-b77ea508e25e
namespace_id                 root

Related Issues/Pull Requests

• [x] Issue #85
• [x] PR #132

  Contributor Checklist

• [x] Add relevant docs to upstream Vault repository, or sufficient reasoning why docs won’t be added yet My Docs PR vault #24941 Link
• [x] Add output for any tests not ran in CI to the PR description (eg, acceptance tests)
• [x] Backwards compatible