gitea: add the gitea token secrets engine (mount, config, teabot roles) (#101)

## Why

teabot's implementer and reviewer bot users should mint **ephemeral, scoped Gitea tokens** on demand rather than holding standing personal access tokens — Gitea tokens never expire on their own, so a leak lasts until someone notices. This registers and mounts the new `vault-plugin-secrets-gitea` engine (released v0.1.0) and declares its roles, mirroring the rancher engine wiring.

## Change

- Register the plugin in the catalog (`config/plugins/vault-plugin-secrets-gitea.yaml`), pinned to the released v0.1.0 binary `sha256 8f67fbc216effada5fd7399888a710b62fad83be0b31761a439e7dec3d56509b` (sha256 of `/opt/openbao-plugins/vault-plugin-secrets-gitea` from the released `openbao-plugin-secrets-gitea-0.1.0` RPM).
- Add `gitea_secret_backend` + `gitea_secret_backend_role` modules and wire them through `config.hcl`, `environments/au/syd1/terragrunt.hcl`, and `modules/vault_cluster` variables/main, using the `giteavaultsecret` provider from the `terraform-unkin` registry (v0.1.0).
- Mount the engine at `gitea/` against `https://git.unkin.net`; seeded site-admin credentials are read from KV (`service/vault/au/syd1/secret_backend/gitea/config`, keys `admin_username`/`admin_password`) — not stored in git.
- **The seed is consumed create-only**: `lifecycle ignore_changes` on `admin_username`/`admin_password` means the engine reads the KV seed only when first creating `gitea/config`. After `rotate-root` diverges the live password from the seed, a later apply never pushes the stale seed back.
- Add roles with conservative, minimal scopes (write: implies read:):
  - `teabot-implementer` — `write:repository`, `write:issue` (clone/push, open PRs, comment).
  - `teabot-reviewer` — `read:repository`, `write:issue` (read diffs, post PR reviews/comments).
- TTLs: `ttl` 1h / `max_ttl` 4h on both roles.

## The site-admin bot + KV seed are now provisioned by Terraform (no manual gap)

Per Ben's review, creating the site-admin bot and seeding its credential is no longer a manual step:

- **terraform-git #46** creates the `gitea-vault-admin` site-admin bot and writes its generated password **once** to `kv/service/vault/au/syd1/secret_backend/gitea/config` (create-only KV write; never updated).
- **terraform-vault #102** grants terraform-git write access to that KV path.

## Ordering (merge + apply)

1. **puppet-prod #498** — installs the plugin binary on the vault nodes (Puppet must run).
2. **terraform-vault #100** (`benvin/gitea-deployer-access`) — deployer access to the gitea mount.
3. **terraform-vault #102** (`benvin/gitea-kv-writer`) — terraform-git KV write grant.
4. **terraform-git #46** (`benvin/gitea-vault-admin`) — creates the bot + seeds KV.
5. **This PR** — mounts the engine (reads the seed) and declares roles.

Files here are disjoint from #100 and #102 (no conflict).

**CI note:** the plan for this PR may hard-fail in CI if the plugin isn't yet registered/installed or the KV seed isn't present in the plan's target. If CI plan fails for that ordering reason, that is expected — do not force; apply only once steps 1–4 are live.

## Remaining manual step (one, ordered)

After this PR's first apply, run `vault write -f gitea/config/rotate-root` so the standing seed password is replaced by one only Vault holds. (On future binary upgrades, bump the RPM version in puppet-prod and the catalog `sha256` here together, then `vault write sys/plugins/reload/backend plugin=vault-plugin-secrets-gitea`.)

https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv
Reviewed-on: #101
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

modules/vault_cluster/main.tf

@@ -421,6 +421,40 @@ module "rancher_secret_backend_role" {
   depends_on = [module.rancher_secret_backend_service_account]
 }
 
+module "gitea_secret_backend" {
+  source = "./modules/gitea_secret_backend"
+
+  for_each = var.gitea_secret_backend
+
+  path                    = each.key
+  plugin                  = each.value.plugin
+  description             = each.value.description
+  gitea_url               = each.value.gitea_url
+  country                 = var.country
+  region                  = var.region
+  ca_cert                 = each.value.ca_cert
+  tls_skip_verify         = each.value.tls_skip_verify
+  request_timeout_seconds = each.value.request_timeout_seconds
+
+  depends_on = [module.plugin]
+}
+
+module "gitea_secret_backend_role" {
+  source = "./modules/gitea_secret_backend_role"
+
+  for_each = var.gitea_secret_backend_role
+
+  backend           = each.value.backend
+  name              = each.value.name
+  username          = each.value.username
+  scopes            = each.value.scopes
+  token_name_prefix = each.value.token_name_prefix
+  ttl               = each.value.ttl
+  max_ttl           = each.value.max_ttl
+
+  depends_on = [module.gitea_secret_backend]
+}
+
 module "vault_policy" {
   source = "./modules/vault_policy"
 

modules/vault_cluster/modules/gitea_secret_backend/main.tf

@@ -0,0 +1,34 @@
+# Mounts the gitea secrets engine and writes its connection config via the
+# giteavaultsecret provider. The plugin is registered ("imported") in the
+# catalog separately (config/plugins/vault-plugin-secrets-gitea.yaml). The
+# seeded site-admin credentials are sensitive and read from KV, not stored in
+# git:
+#   kv/service/vault/<country>/<region>/secret_backend/<path>/config
+# Expected keys: admin_username (required), admin_password (required).
+data "vault_kv_secret_v2" "config" {
+  mount = "kv"
+  name  = "service/vault/${var.country}/${var.region}/secret_backend/${var.path}/config"
+}
+
+resource "gitea_secret_backend" "this" {
+  path                    = var.path
+  plugin                  = var.plugin
+  description             = var.description
+  gitea_url               = var.gitea_url
+  admin_username          = data.vault_kv_secret_v2.config.data["admin_username"]
+  admin_password          = data.vault_kv_secret_v2.config.data["admin_password"]
+  ca_cert                 = var.ca_cert
+  tls_skip_verify         = var.tls_skip_verify
+  request_timeout_seconds = var.request_timeout_seconds
+
+  lifecycle {
+    # The KV seed is a bootstrap credential: it is consumed only when the engine
+    # config is first created. After creation the live admin password is rotated
+    # in place (vault write -f gitea/config/rotate-root) and diverges from the
+    # seed, so re-reading the (possibly stale) KV value must never push it back.
+    # Ignoring the credential attributes makes this module create-only for them.
+    # (The sibling rancher/litellm seed modules do not yet do this and would
+    # re-push their seed on a subsequent apply.)
+    ignore_changes = [admin_username, admin_password]
+  }
+}

modules/vault_cluster/modules/gitea_secret_backend/terraform.tf

@@ -0,0 +1,13 @@
+terraform {
+  required_version = ">= 1.10"
+  required_providers {
+    vault = {
+      source  = "hashicorp/vault"
+      version = "5.6.0"
+    }
+    gitea = {
+      source  = "artifactapi.k8s.syd1.au.unkin.net/terraform-unkin/giteavaultsecret"
+      version = "0.1.0"
+    }
+  }
+}

modules/vault_cluster/modules/gitea_secret_backend/variables.tf

@@ -0,0 +1,49 @@
+variable "path" {
+  description = "Mount path of the gitea secrets engine (e.g. \"gitea\")"
+  type        = string
+}
+
+variable "plugin" {
+  description = "Registered plugin name to mount (the catalog name = mount type)"
+  type        = string
+  default     = "vault-plugin-secrets-gitea"
+}
+
+variable "description" {
+  description = "Human-friendly description of the mount"
+  type        = string
+  default     = null
+}
+
+variable "gitea_url" {
+  description = "Base URL of the Gitea server (e.g. https://git.unkin.net)"
+  type        = string
+}
+
+variable "country" {
+  description = "Country segment of the KV path holding the seeded admin credentials"
+  type        = string
+}
+
+variable "region" {
+  description = "Region segment of the KV path holding the seeded admin credentials"
+  type        = string
+}
+
+variable "ca_cert" {
+  description = "PEM CA certificate that signed the Gitea server's TLS cert (optional; omit to use the system trust store)"
+  type        = string
+  default     = null
+}
+
+variable "tls_skip_verify" {
+  description = "Skip TLS verification of the Gitea server (not recommended)"
+  type        = bool
+  default     = false
+}
+
+variable "request_timeout_seconds" {
+  description = "HTTP timeout in seconds for calls from the plugin to Gitea"
+  type        = number
+  default     = 30
+}

modules/vault_cluster/modules/gitea_secret_backend_role/main.tf

@@ -0,0 +1,12 @@
+# A role that mints short-lived, scoped gitea tokens for a target Gitea user.
+# Reading gitea/creds/<name> produces a lease-bound token that is deleted from
+# Gitea when the lease is revoked or reaches max_ttl.
+resource "gitea_secret_backend_role" "this" {
+  backend           = var.backend
+  name              = var.name
+  username          = var.username
+  scopes            = var.scopes
+  token_name_prefix = var.token_name_prefix
+  ttl               = var.ttl
+  max_ttl           = var.max_ttl
+}

modules/vault_cluster/modules/gitea_secret_backend_role/terraform.tf

@@ -0,0 +1,9 @@
+terraform {
+  required_version = ">= 1.10"
+  required_providers {
+    gitea = {
+      source  = "artifactapi.k8s.syd1.au.unkin.net/terraform-unkin/giteavaultsecret"
+      version = "0.1.0"
+    }
+  }
+}

modules/vault_cluster/modules/gitea_secret_backend_role/variables.tf

@@ -0,0 +1,37 @@
+variable "backend" {
+  description = "Mount path of the gitea secrets engine this role belongs to"
+  type        = string
+}
+
+variable "name" {
+  description = "Role name (read gitea/creds/<name> to mint a token)"
+  type        = string
+}
+
+variable "username" {
+  description = "Target Gitea username the minted tokens belong to"
+  type        = string
+}
+
+variable "scopes" {
+  description = "Gitea access-token scopes granted to minted tokens (write: implies read:)"
+  type        = list(string)
+}
+
+variable "token_name_prefix" {
+  description = "Prefix for the generated Gitea token name (optional)"
+  type        = string
+  default     = null
+}
+
+variable "ttl" {
+  description = "Default lease TTL in seconds for minted tokens"
+  type        = number
+  default     = null
+}
+
+variable "max_ttl" {
+  description = "Maximum lease TTL in seconds for minted tokens"
+  type        = number
+  default     = null
+}

modules/vault_cluster/variables.tf

@@ -388,6 +388,33 @@ variable "rancher_secret_backend_role" {
   default = {}
 }
 
+variable "gitea_secret_backend" {
+  description = "Map of gitea token secret engines to create (mount + config; seeded admin creds read from KV)"
+  type = map(object({
+    plugin                  = optional(string, "vault-plugin-secrets-gitea")
+    description             = optional(string)
+    gitea_url               = string
+    ca_cert                 = optional(string)
+    tls_skip_verify         = optional(bool, false)
+    request_timeout_seconds = optional(number, 30)
+  }))
+  default = {}
+}
+
+variable "gitea_secret_backend_role" {
+  description = "Map of gitea token-minting roles to create"
+  type = map(object({
+    name              = string
+    backend           = string
+    username          = string
+    scopes            = list(string)
+    token_name_prefix = optional(string)
+    ttl               = optional(number)
+    max_ttl           = optional(number)
+  }))
+  default = {}
+}
+
 variable "policy_auth_map" {
   description = "Map of auth mounts -> auth roles -> policy names"
   type        = map(map(list(string)))