Add Authentik OIDC SSO as the default human login for OpenBao

Human access to OpenBao is LDAP-only today, so operators carry a second set of
credentials outside Authentik and group membership is maintained twice. This
makes Authentik SSO the offered default on the UI login page and gives
`bao login -method=oidc` a working CLI path, while approle and kubernetes (CI
and agents) plus the break-glass root path are untouched.

Add three modules mirroring the auth_ldap_* structure: auth_oidc_backend mounts
a vault_jwt_auth_backend of type oidc, auth_oidc_role creates the default login
role, and auth_oidc_group creates an external vault_identity_group plus its
group alias so IdP groups map onto policies.

Mount the backend at the literal path "oidc". The Authentik provider registers
strict redirect URIs containing /ui/vault/auth/oidc/oidc/callback, so the path
is load-bearing and must not be renamed.

Read client_id and client_secret from kv/service/authentik/oidc-vault, which
terraform-authentik generates and writes; nothing is seeded by hand.

Match groups on the ak_groups claim rather than groups, because Authentik's
default profile mapping only emits direct memberships and the estate nests
akP-* permission groups under akR-* roles.

Bind akP-vault-admin to global-root, the same policy the LDAP vault_admin group
already carries. Only akP-* permission groups are named in config or policy;
akR-* roles stay grouping-only.

Grant the deployer auth/oidc/* and identity group management, both of which it
currently lacks. AppRole capabilities are fixed at login, so these land in an
apply before the resources that need them.

modules/vault_cluster/main.tf

@@ -64,6 +64,55 @@ module "auth_ldap_group" {
   depends_on = [module.auth_ldap_backend]
 }
 
+module "auth_oidc_backend" {
+  source = "./modules/auth_oidc_backend"
+
+  for_each = var.auth_oidc_backend
+
+  path                = each.key
+  description         = each.value.description
+  oidc_discovery_url  = each.value.oidc_discovery_url
+  client_secret_mount = each.value.client_secret_mount
+  client_secret_path  = each.value.client_secret_path
+  default_role        = each.value.default_role
+  listing_visibility  = each.value.listing_visibility
+  default_lease_ttl   = each.value.default_lease_ttl
+  max_lease_ttl       = each.value.max_lease_ttl
+}
+
+module "auth_oidc_role" {
+  source = "./modules/auth_oidc_role"
+
+  for_each = var.auth_oidc_role
+
+  backend               = each.value.backend
+  role_name             = each.value.role_name
+  user_claim            = each.value.user_claim
+  groups_claim          = each.value.groups_claim
+  oidc_scopes           = each.value.oidc_scopes
+  bound_audiences       = each.value.bound_audiences
+  allowed_redirect_uris = each.value.allowed_redirect_uris
+  token_ttl             = each.value.token_ttl
+  token_max_ttl         = each.value.token_max_ttl
+  # Human authorization comes from the external identity groups below, so a
+  # login role carrying no policies is the normal case.
+  token_policies = try(var.policy_auth_map[each.value.backend][each.value.role_name], [])
+
+  depends_on = [module.auth_oidc_backend]
+}
+
+module "auth_oidc_group" {
+  source = "./modules/auth_oidc_group"
+
+  for_each = var.auth_oidc_group
+
+  groupname      = each.value.groupname
+  policies       = var.policy_auth_map[each.value.backend][each.value.groupname]
+  mount_accessor = module.auth_oidc_backend[each.value.backend].accessor
+
+  depends_on = [module.auth_oidc_backend]
+}
+
 module "auth_kubernetes_backend" {
   source = "./modules/auth_kubernetes_backend"
 

modules/vault_cluster/modules/auth_oidc_backend/main.tf

@@ -0,0 +1,22 @@
+# Expected keys in KV secret: client_id, client_secret (generated and written by
+# terraform-authentik's oauth2 provider module, never seeded by hand).
+data "vault_kv_secret_v2" "oidc_client" {
+  mount = var.client_secret_mount
+  name  = var.client_secret_path
+}
+
+resource "vault_jwt_auth_backend" "oidc" {
+  path               = var.path
+  type               = "oidc"
+  description        = var.description
+  oidc_discovery_url = var.oidc_discovery_url
+  oidc_client_id     = data.vault_kv_secret_v2.oidc_client.data["client_id"]
+  oidc_client_secret = data.vault_kv_secret_v2.oidc_client.data["client_secret"]
+  default_role       = var.default_role
+
+  tune {
+    default_lease_ttl  = var.default_lease_ttl
+    max_lease_ttl      = var.max_lease_ttl
+    listing_visibility = var.listing_visibility
+  }
+}

modules/vault_cluster/modules/auth_oidc_backend/outputs.tf

@@ -0,0 +1,9 @@
+output "accessor" {
+  description = "Accessor of the OIDC auth mount, used to bind identity group aliases"
+  value       = vault_jwt_auth_backend.oidc.accessor
+}
+
+output "path" {
+  description = "Mount path of the OIDC auth backend"
+  value       = vault_jwt_auth_backend.oidc.path
+}

modules/vault_cluster/modules/auth_oidc_backend/terraform.tf

@@ -0,0 +1,9 @@
+terraform {
+  required_version = ">= 1.10"
+  required_providers {
+    vault = {
+      source  = "hashicorp/vault"
+      version = "5.6.0"
+    }
+  }
+}

modules/vault_cluster/modules/auth_oidc_backend/variables.tf

@@ -0,0 +1,56 @@
+variable "path" {
+  description = "Mount path of the OIDC auth backend"
+  type        = string
+  default     = "oidc"
+}
+
+variable "description" {
+  description = "Human-readable description of the auth mount"
+  type        = string
+  default     = null
+}
+
+variable "oidc_discovery_url" {
+  description = "OIDC issuer discovery URL of the identity provider"
+  type        = string
+}
+
+variable "client_secret_mount" {
+  description = "KV-v2 mount holding the OIDC client credentials"
+  type        = string
+  default     = "kv"
+}
+
+variable "client_secret_path" {
+  description = "Path within the KV-v2 mount holding client_id and client_secret"
+  type        = string
+  default     = "service/authentik/oidc-vault"
+}
+
+variable "default_role" {
+  description = "Role used when none is supplied at login (the UI/CLI default)"
+  type        = string
+  default     = "default"
+}
+
+variable "listing_visibility" {
+  description = "Specifies whether to show this mount in the UI-specific listing endpoint. Valid values are 'unauth' or 'hidden'"
+  type        = string
+  default     = null
+  validation {
+    condition     = var.listing_visibility == null || contains(["unauth", "hidden"], var.listing_visibility)
+    error_message = "listing_visibility must be either 'unauth' or 'hidden'."
+  }
+}
+
+variable "default_lease_ttl" {
+  description = "Specifies the default time-to-live. If set, this overrides the global default. Must be a valid duration string"
+  type        = string
+  default     = null
+}
+
+variable "max_lease_ttl" {
+  description = "Specifies the maximum time-to-live. If set, this overrides the global default. Must be a valid duration string"
+  type        = string
+  default     = null
+}

modules/vault_cluster/modules/auth_oidc_group/main.tf

@@ -0,0 +1,13 @@
+# External identity group: membership is asserted by the IdP through the role's
+# groups_claim, matched by the alias name below.
+resource "vault_identity_group" "group" {
+  name     = var.groupname
+  type     = "external"
+  policies = var.policies
+}
+
+resource "vault_identity_group_alias" "alias" {
+  name           = var.groupname
+  mount_accessor = var.mount_accessor
+  canonical_id   = vault_identity_group.group.id
+}

modules/vault_cluster/modules/auth_oidc_group/terraform.tf

@@ -0,0 +1,9 @@
+terraform {
+  required_version = ">= 1.10"
+  required_providers {
+    vault = {
+      source  = "hashicorp/vault"
+      version = "5.6.0"
+    }
+  }
+}

modules/vault_cluster/modules/auth_oidc_group/variables.tf

@@ -0,0 +1,14 @@
+variable "groupname" {
+  description = "Name of the IdP group, as it appears in the groups claim"
+  type        = string
+}
+
+variable "policies" {
+  description = "List of policies to assign to the identity group"
+  type        = list(string)
+}
+
+variable "mount_accessor" {
+  description = "Accessor of the OIDC auth mount the alias is bound to"
+  type        = string
+}

modules/vault_cluster/modules/auth_oidc_role/main.tf

@@ -0,0 +1,13 @@
+resource "vault_jwt_auth_backend_role" "role" {
+  backend               = var.backend
+  role_name             = var.role_name
+  role_type             = "oidc"
+  user_claim            = var.user_claim
+  groups_claim          = var.groups_claim
+  oidc_scopes           = var.oidc_scopes
+  bound_audiences       = var.bound_audiences
+  allowed_redirect_uris = var.allowed_redirect_uris
+  token_ttl             = var.token_ttl
+  token_max_ttl         = var.token_max_ttl
+  token_policies        = var.token_policies
+}

modules/vault_cluster/modules/auth_oidc_role/terraform.tf

@@ -0,0 +1,9 @@
+terraform {
+  required_version = ">= 1.10"
+  required_providers {
+    vault = {
+      source  = "hashicorp/vault"
+      version = "5.6.0"
+    }
+  }
+}

modules/vault_cluster/modules/auth_oidc_role/variables.tf

@@ -0,0 +1,56 @@
+variable "backend" {
+  description = "The unique path of the OIDC auth backend to configure"
+  type        = string
+}
+
+variable "role_name" {
+  description = "The name of the role"
+  type        = string
+}
+
+variable "user_claim" {
+  description = "Claim used as the entity alias name (the Vault identity of the human)"
+  type        = string
+  default     = "email"
+}
+
+variable "groups_claim" {
+  description = "Claim holding the caller's group memberships, matched against identity group aliases"
+  type        = string
+  default     = "ak_groups"
+}
+
+variable "oidc_scopes" {
+  description = "Scopes requested from the identity provider during the authorization request"
+  type        = list(string)
+  default     = []
+}
+
+variable "bound_audiences" {
+  description = "List of audiences (aud claim) accepted in the ID token"
+  type        = list(string)
+  default     = []
+}
+
+variable "allowed_redirect_uris" {
+  description = "Redirect URIs accepted for this role. Must match the provider's registered URIs exactly"
+  type        = list(string)
+}
+
+variable "token_ttl" {
+  description = "The TTL period of tokens issued using this role, in seconds"
+  type        = number
+  default     = 3600
+}
+
+variable "token_max_ttl" {
+  description = "The maximum lifetime for generated tokens in number of seconds. Its current value will be referenced at renewal time."
+  type        = number
+  default     = 28800
+}
+
+variable "token_policies" {
+  description = "List of policies to assign to the role (passed from policy_auth_map). Human authorization normally comes from external identity groups instead"
+  type        = list(string)
+  default     = []
+}

modules/vault_cluster/variables.tf

@@ -62,6 +62,46 @@ variable "auth_ldap_group" {
   default = {}
 }
 
+variable "auth_oidc_backend" {
+  description = "Map of OIDC (JWT) auth backends to create"
+  type = map(object({
+    oidc_discovery_url  = string
+    description         = optional(string)
+    client_secret_mount = optional(string, "kv")
+    client_secret_path  = optional(string, "service/authentik/oidc-vault")
+    default_role        = optional(string, "default")
+    listing_visibility  = optional(string)
+    default_lease_ttl   = optional(string)
+    max_lease_ttl       = optional(string)
+  }))
+  default = {}
+}
+
+variable "auth_oidc_role" {
+  description = "Map of OIDC auth roles to create"
+  type = map(object({
+    role_name             = string
+    backend               = string
+    allowed_redirect_uris = list(string)
+    user_claim            = optional(string, "email")
+    groups_claim          = optional(string, "ak_groups")
+    oidc_scopes           = optional(list(string), [])
+    bound_audiences       = optional(list(string), [])
+    token_ttl             = optional(number, 3600)
+    token_max_ttl         = optional(number, 28800)
+  }))
+  default = {}
+}
+
+variable "auth_oidc_group" {
+  description = "Map of external identity groups bound to an OIDC auth mount"
+  type = map(object({
+    groupname = string
+    backend   = string
+  }))
+  default = {}
+}
+
 variable "auth_kubernetes_backend" {
   description = "Map of Kubernetes auth backends to create"
   type = map(object({