headscale/hscontrol/api/v2

API v2: Headscale's v2 API

This is Headscale's v2 HTTP API, served at /api/v2. Some of its endpoints are ported from Tailscale's API, reusing Tailscale's wire shapes, so the Tailscale ecosystem that cannot talk to Headscale today works: the Terraform/OpenTofu provider, tscli, and the official Go client (tailscale.com/client/tailscale/v2).

It is not a port of the whole Tailscale API. Ported endpoints are added one at a time, only as we need them; a headscale-native v2 endpoint may use headscale's own conventions. The headscale-native admin API stays at /api/v1 (hscontrol/api/v1). This guide is for the endpoints ported from Tailscale.

Conventions

• Operations derived from Tailscale carry the Tailscale compat tag.
• The {tailnet} path segment must be - (the single Headscale tailnet); anything else is 404. See requireDefaultTailnet.
• Errors use Tailscale's body ({"message","data","status"}), installed as a per-API transform (tailscaleErrorTransformer in errors.go). A future headscale-native v2 operation would keep Huma's RFC 9457 problem+json.
• Auth accepts a credential as HTTP Basic (key as username, what the SDK sends) or Bearer: an admin API key (hskey-api-…), or an OAuth access token (hskey-oauthtok-…). See authMiddleware.
• Each operation declares the Tailscale scope it requires (auth_keys, oauth_keys, devices:core, devices:routes, policy_file, feature_settings, each with a :read subset, plus all/all:read). requireScope records it both for the middleware and in the generated OpenAPI, as an x-required-scope extension and a sentence in the operation description, so the scope shows up in the docs and spec. Enforcement: an admin API key is all-access (scope checks skipped); an OAuth access token is scope-limited, the middleware checks the operation's declared scope against the token's grant (scope.Grants, where a write scope subsumes its :read and all/all:read are super-scopes). The two are told apart by credential prefix.
• Resolve one entity by id with a typed getter (GetNodeByID, GetUserByID, GetAPIKeyByID, GetPreAuthKeyByID); add one to state/db if it is missing rather than scanning a List. Build responses from the view accessors (NodeView/UserView/PreAuthKeyView), never AsStruct().
• Reuse upstream wire shapes, but declare the request/response structs here: Huma reflects these to build the OpenAPI schema, and the upstream Key's ExpirySeconds *time.Duration marshals as nanoseconds, which the spec and every client read as seconds.

OAuth clients & scopes

Most of the Tailscale ecosystem (the Terraform provider, tscli, the Go client) accepts either an API key or OAuth 2.0 client-credentials; the Kubernetes operator is OAuth-only. Supporting OAuth lets all of them drive Headscale.

• OAuth clients are not a separate resource; they are keyType:"client" on the keys endpoint, exactly as Tailscale does it. Create (POST /api/v2/tailnet/-/keys with {"keyType":"client","scopes":[…],"tags":[…]}) returns a Key whose id is the client id and whose key is the secret, shown once; get/list never re-expose it. The secret is hskey-client-<clientID>-<secret>, embedding the client id so the token endpoint derives it from the secret (Tailscale's get-authkey trick). See keys.go (createOAuthClient) and db/oauth.go.
• Token endpoint POST /api/v2/oauth/token (oauth.go) is a plain handler, not a Huma operation: it takes application/x-www-form-urlencoded and emits RFC 6749 OAuth2 error bodies ({"error","error_description"}). Credentials arrive in the body or HTTP Basic; optional space-delimited scope/tags narrow the token to a subset of the client's grant. It returns a 1-hour Bearer access token (hskey-oauthtok-…).
• Scope enforcement is the one seam in authMiddleware. Tag enforcement: an auth key minted by a token may only carry tags the token holds, or tags owned-by them via the policy tagOwners (State.TagOwnedByTags → policy/v2), so e.g. an operator token tagged tag:k8s-operator may mint tag:k8s keys.
• Credentials/tokens are stored like API keys: a public id/prefix plus an Argon2id hash of the secret (no JWT, no signing keys). OAuthClient and OAuthAccessToken live in types/oauth.go and db/oauth.go.

Adding an endpoint

Worked example: the keys resource (keys.go) = Tailscale auth keys = Headscale pre-auth keys.

1. Read the Tailscale spec. Find the operation in the Tailscale API reference (OpenAPI 3.1). Note method, path, request/response schema, and which variant(s) Headscale supports (auth keys only, for keys).

2. Capture golden samples. Pull the request + response JSON examples from the spec, prune to the variant, and use them as the assertion in the contract test. Acceptance: the captured request and response are recorded in the test.

3. Map to Headscale. Write the field ↔ field ↔ state call mapping. Record gaps and the decision for each (e.g. Tailscale preauthorized has no Headscale equivalent: accepted, ignored, echoed back). Acceptance: every request field is consumed or deliberately ignored; every response field has a source.

4. Implement the Huma operation. Declare named request/response structs with validation/default/example/doc tags; tag the operation Tailscale compat; declare its Errors; enforce the tailnet and scope. Map state errors with mapError. Acceptance: go build ./hscontrol/api/v2/ and the operation appears in Spec().

5. Contract test (in-process, humatest). Assert the server accepts the golden request and returns the golden response shape, with secrets and timestamps neutralised. Pin the wire facts (e.g. expirySeconds in seconds, the list {"keys":[...]} envelope, the error message). See hscontrol/apiv2_keys_test.go. Acceptance: the test is green.

6. Roundtrip the real clients. Add a t.Run subtest to TestAPIv2 (hscontrol/servertest/apiv2_test.go) for each of the Go client, tscli, and OpenTofu, full create→read→list→delete against one shared server on a real loopback port (servertest.WithRealListener). tscli and tofu come from the nix dev shell; a missing binary fails the test. Acceptance: nix develop -c go test ./hscontrol/servertest/ -run TestAPIv2 is green.

7. Update the CLI only if the v2 operation fully replaces a v1 one. Tailscale has no separate key-expire verb (its DELETE is the revoke), so v2 maps DELETE to a soft revoke: the key stays retrievable with invalid: true until the collector reaps it (preauth_keys.revoked_retention), the equivalent of v1 preauthkeys expire. headscale preauthkeys still stays on v1 for now (it is the cross-user admin surface), but the verb gap that previously blocked migration is closed.