Release 0.12.0: CloudFlare Turnstile on OTC email-entry

backend/.env.example

@@ -92,3 +92,21 @@ OTC_TTL_MINUTES=10
 # loud-failure shape so the abuse path is visible). Set to 0 to
 # disable the cooldown — useful for tests but never in production.
 OTC_REQUEST_COOLDOWN_SECONDS=60
+
+# --- v0.12.0: CloudFlare Turnstile gate on OTC dispatch (§6.2, item #10) ---
+# Provision a Turnstile site at dash.cloudflare.com → Turnstile → Add
+# site. The site key (public) goes in `frontend/.env` as
+# VITE_TURNSTILE_SITE_KEY. The secret key (private) goes here and is
+# what the backend POSTs to /siteverify alongside the user's response
+# token. Leave both unset for dev/test paths; the gate stays open when
+# the secret is absent AND TURNSTILE_REQUIRED=false (the default).
+CLOUDFLARE_TURNSTILE_SECRET=
+
+# When `true`, /auth/otc/request fails closed (HTTP 500 "auth
+# misconfigured") if CLOUDFLARE_TURNSTILE_SECRET is unset. When `false`
+# (the default), a missing secret skips verification — useful in dev
+# and during the pre-rollout window when the operator hasn't wired
+# the secret yet. Flip to `true` once the secret is wired so a future
+# config drift surfaces as a loud 500 rather than a silent abuse-
+# defense disablement.
+TURNSTILE_REQUIRED=false

backend/app/main.py

@@ -27,6 +27,7 @@ from . import (
     otc,
     passcode as passcode_mod,
     providers as providers_mod,
+    turnstile,
     webhooks,
 )
 from .bot import Bot
@@ -39,6 +40,14 @@ log = logging.getLogger("rfc_app")
 
 class OtcRequestBody(BaseModel):
     email: str = Field(min_length=3, max_length=320)
+    # v0.12.0 / roadmap item #10: CloudFlare Turnstile token from the
+    # frontend widget. Optional in the body so a deployment that has
+    # not yet wired the Turnstile site key (or a dev environment with
+    # the widget intentionally skipped) still routes through the same
+    # endpoint; the backend turnstile.verify_token call decides whether
+    # to admit the request based on `TURNSTILE_REQUIRED` + presence of
+    # the secret.
+    turnstile_token: str | None = Field(default=None, max_length=4096)
 
 
 class OtcVerifyBody(BaseModel):
@@ -215,7 +224,27 @@ def _oauth_router(config) -> APIRouter:
     # ---------------------------------------------------------------
 
     @router.post("/auth/otc/request")
-    async def otc_request(body: OtcRequestBody):
+    async def otc_request(body: OtcRequestBody, request: Request):
+        # v0.12.0 / roadmap item #10: gate the request on a successful
+        # Turnstile siteverify before the bcrypt hash + SMTP send. The
+        # check runs first so a failed challenge spends no rate budget
+        # and produces no envelope. When the operator has not wired the
+        # secret AND TURNSTILE_REQUIRED=false (the default), the gate
+        # opens — see `backend/app/turnstile.py` for the full matrix.
+        client_ip = request.client.host if request.client else None
+        ts = turnstile.verify_token(body.turnstile_token, client_ip=client_ip)
+        if not ts.ok:
+            if ts.reason == "misconfigured":
+                # TURNSTILE_REQUIRED=true but the secret is unset. This
+                # is an operator/config problem, not a client problem;
+                # surface as 500 so the operator notices in their logs
+                # rather than blaming the user's browser.
+                raise HTTPException(500, "auth misconfigured")
+            # missing-token / failed / network → uniform 400 so the
+            # response does not enumerate which leg of the challenge
+            # broke. The reason is in the server logs.
+            raise HTTPException(400, "verification failed")
+
         outcome = otc.request_code(body.email)
         if outcome.reason == "cooldown":
             # Loud failure per the rate-limit primitive — the abuse

backend/app/turnstile.py

@@ -0,0 +1,148 @@
+"""§6.2 / v0.12.0 / roadmap item #10: CloudFlare Turnstile siteverify.
+
+The OTC request endpoint (`/auth/otc/request`) is the abuse hot path
+of the auth surface since v0.7.0 — the per-email cooldown stops the
+trivial back-to-back loop, but it does not stop a distributed scraper
+that fans out across a large invitee list to harvest the "this email
+is admitted vs. this email is not" signal indirectly (timing
+differences, SMTP bounce-rate observation). v0.12.0 gates the request
+endpoint behind a one-step browser-side Turnstile challenge before the
+bcrypt hash + SMTP send.
+
+Stateless: no DB writes, no schema change. The siteverify call to
+CloudFlare lives entirely in this module; the endpoint handler in
+`main.py` thin-wraps `verify_token`.
+
+Tunables (read at call time so tests can monkeypatch):
+
+  * `CLOUDFLARE_TURNSTILE_SECRET`  — the operator-provisioned secret
+    key from the Turnstile dashboard. Lives in GCP Secret Manager in
+    production; absent in tests (which monkeypatch the siteverify
+    transport). When unset, the behavior depends on `TURNSTILE_REQUIRED`:
+      - `TURNSTILE_REQUIRED=true`  → fail closed (`misconfigured`).
+      - `TURNSTILE_REQUIRED=false` (default) → skip verification entirely
+        and admit the request. This is the dev/test path and the
+        "operator hasn't wired the secret yet" path; production
+        deployments **should** set `TURNSTILE_REQUIRED=true` once the
+        secret is in place so a regression in the secret wiring fails
+        loudly instead of silently disabling abuse defense.
+
+  * `TURNSTILE_REQUIRED`           — `true` / `false` (default `false`).
+    When `false` and the secret is absent, the gate is open. When
+    `true` and the secret is absent, the endpoint refuses with a
+    misconfigured-auth shape rather than silently letting requests
+    through.
+
+  * `TURNSTILE_SITEVERIFY_URL`     — points at the real CloudFlare
+    endpoint by default. Override in tests to redirect at a mock
+    URL when `httpx.MockTransport` isn't ergonomic for the case.
+
+The siteverify contract is documented at
+https://developers.cloudflare.com/turnstile/get-started/server-side-validation/.
+We POST `secret` + `response` (and optionally `remoteip`) as form
+fields and read back `{"success": true|false, ...}`. Any network /
+parse failure on the siteverify call is treated as a verification
+failure (`network`) — the abuse path is to skip the challenge, so
+"can't reach CloudFlare" defaults to "refuse the request" when
+`TURNSTILE_REQUIRED=true`, and "admit" when `TURNSTILE_REQUIRED=false`.
+"""
+from __future__ import annotations
+
+import logging
+import os
+from dataclasses import dataclass
+
+import httpx
+
+log = logging.getLogger(__name__)
+
+
+SITEVERIFY_URL = "https://challenges.cloudflare.com/turnstile/v0/siteverify"
+
+
+def _secret() -> str:
+    return os.environ.get("CLOUDFLARE_TURNSTILE_SECRET", "").strip()
+
+
+def _required() -> bool:
+    raw = os.environ.get("TURNSTILE_REQUIRED", "").strip().lower()
+    return raw in ("1", "true", "yes", "on")
+
+
+def _siteverify_url() -> str:
+    return os.environ.get("TURNSTILE_SITEVERIFY_URL", "").strip() or SITEVERIFY_URL
+
+
+@dataclass
+class VerifyOutcome:
+    """Result of a Turnstile siteverify call.
+
+    `ok`: the request **may proceed**. True both for "siteverify said
+    success" and for "no secret configured AND not required" (the
+    dev/test soft-fail path).
+
+    `reason`: one of
+      * 'ok'             — siteverify returned success.
+      * 'skipped'        — no secret configured, TURNSTILE_REQUIRED=false.
+                            The gate is open; the endpoint admits the request.
+      * 'misconfigured'  — TURNSTILE_REQUIRED=true but no secret in env.
+                            The endpoint fails closed with 500.
+      * 'missing-token'  — the client did not send a token at all and
+                            verification is required.
+      * 'failed'         — siteverify returned success=false. The
+                            endpoint refuses with 400.
+      * 'network'        — siteverify call raised. Treated as a failure
+                            under TURNSTILE_REQUIRED=true.
+    """
+    ok: bool
+    reason: str
+
+
+def verify_token(token: str | None, *, client_ip: str | None = None) -> VerifyOutcome:
+    """Validate a Turnstile token against CloudFlare's siteverify endpoint.
+
+    Returns a VerifyOutcome describing whether the calling endpoint
+    should proceed. The endpoint maps `ok=False` to an HTTP status per
+    the `reason`:
+
+      * 'misconfigured' → 500 "auth misconfigured"
+      * 'missing-token' / 'failed' / 'network' → 400 "verification failed"
+
+    Tests monkeypatch `httpx.post` (or set `TURNSTILE_SITEVERIFY_URL`
+    + a MockTransport client) to avoid touching the real CloudFlare
+    endpoint. No real keys are ever embedded in tests.
+    """
+    secret = _secret()
+    required = _required()
+
+    if not secret:
+        if required:
+            log.warning("Turnstile required but CLOUDFLARE_TURNSTILE_SECRET is unset; failing closed")
+            return VerifyOutcome(ok=False, reason="misconfigured")
+        # Dev/test/soft-fail path: no secret, not required → gate is open.
+        return VerifyOutcome(ok=True, reason="skipped")
+
+    if not token or not token.strip():
+        # Secret is set, so verification is in force. A missing token
+        # is a hard refuse — the frontend should have rendered the
+        # widget and collected one.
+        return VerifyOutcome(ok=False, reason="missing-token")
+
+    data = {"secret": secret, "response": token.strip()}
+    if client_ip:
+        data["remoteip"] = client_ip
+
+    try:
+        response = httpx.post(_siteverify_url(), data=data, timeout=10.0)
+        payload = response.json()
+    except Exception as exc:  # network, JSON parse, etc.
+        log.warning("Turnstile siteverify call failed: %s", exc)
+        return VerifyOutcome(ok=False, reason="network")
+
+    if payload.get("success") is True:
+        return VerifyOutcome(ok=True, reason="ok")
+
+    # `error-codes` is a list of strings on failure; we log the codes
+    # for the operator without surfacing them to the client.
+    log.info("Turnstile siteverify rejected token: %s", payload.get("error-codes"))
+    return VerifyOutcome(ok=False, reason="failed")

backend/tests/test_turnstile_vertical.py

@@ -0,0 +1,220 @@
+"""End-to-end integration tests for the v0.12.0 CloudFlare Turnstile
+gate on `/auth/otc/request` (§6.2 / roadmap item #10).
+
+The release gates the OTC request endpoint behind a one-step
+browser-side Turnstile challenge before the bcrypt hash + SMTP send.
+The tests prove:
+
+  * Happy path: with the secret set, a valid token admits the request
+    and the OTC envelope lands.
+  * Failure path: with the secret set, a token siteverify rejects
+    refuses the request with 400 and produces no envelope.
+  * Missing-token: with the secret set, a request without a token
+    refuses with 400.
+  * Missing-secret-soft: with the secret unset AND
+    `TURNSTILE_REQUIRED=false` (the v0.12.0 default), the request
+    admits — this is the dev / "operator hasn't wired it yet" path.
+  * Missing-secret-hard: with the secret unset AND
+    `TURNSTILE_REQUIRED=true`, the request refuses with 500
+    "auth misconfigured" — the production fail-closed path once
+    the operator has flipped the policy.
+
+The Turnstile siteverify call is mocked at the `httpx.post` boundary
+inside `app.turnstile` so no real keys are needed and no real
+CloudFlare call is made. The Gitea fakes from `test_propose_vertical`
+remain in scope so the rest of the app boots cleanly.
+"""
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+import pytest
+
+from test_propose_vertical import (  # noqa: F401
+    FakeGitea,
+    app_with_fake_gitea,
+    tmp_env,
+)
+
+
+def _reset_outbound():
+    from app import email as email_mod
+    email_mod.reset_sent_envelopes()
+
+
+def _outbound_otc_envelopes(to_address: str | None = None) -> list[dict]:
+    from app import email as email_mod
+    out = []
+    for env in email_mod.sent_envelopes():
+        if env.get("kind") != "otc":
+            continue
+        if to_address is not None and env["to"] != to_address:
+            continue
+        out.append(env)
+    return out
+
+
+def _patch_siteverify(monkeypatch, *, success: bool, error_codes: list[str] | None = None):
+    """Replace `httpx.post` inside `app.turnstile` with a stub that
+    returns the requested success shape. The stub does not touch the
+    real CloudFlare endpoint and never sees a real secret.
+    """
+    captured = {}
+
+    def fake_post(url, *, data=None, timeout=None, **kwargs):
+        captured["url"] = url
+        captured["data"] = data
+        body = {"success": bool(success)}
+        if error_codes is not None:
+            body["error-codes"] = error_codes
+        return SimpleNamespace(json=lambda: body)
+
+    from app import turnstile as turnstile_mod
+    monkeypatch.setattr(turnstile_mod.httpx, "post", fake_post)
+    return captured
+
+
+# ---------------------------------------------------------------------------
+# Happy path: secret set, token valid → admit + OTC envelope lands
+# ---------------------------------------------------------------------------
+
+
+def test_otc_request_admits_when_turnstile_token_is_valid(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    monkeypatch.setenv("CLOUDFLARE_TURNSTILE_SECRET", "test-secret-not-real")
+    monkeypatch.setenv("TURNSTILE_REQUIRED", "true")
+    captured = _patch_siteverify(monkeypatch, success=True)
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        _reset_outbound()
+        r = client.post(
+            "/auth/otc/request",
+            json={"email": "alice@example.com", "turnstile_token": "fake-token-abc"},
+        )
+        assert r.status_code == 200, r.text
+        # The siteverify call was made with the secret + the token we sent.
+        assert captured["data"]["secret"] == "test-secret-not-real"
+        assert captured["data"]["response"] == "fake-token-abc"
+        # And the OTC dispatch ran — exactly one envelope to the address.
+        envs = _outbound_otc_envelopes("alice@example.com")
+        assert len(envs) == 1
+
+
+# ---------------------------------------------------------------------------
+# Failure path: secret set, siteverify says success=false → 400 + no envelope
+# ---------------------------------------------------------------------------
+
+
+def test_otc_request_refuses_when_turnstile_siteverify_fails(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    monkeypatch.setenv("CLOUDFLARE_TURNSTILE_SECRET", "test-secret-not-real")
+    monkeypatch.setenv("TURNSTILE_REQUIRED", "true")
+    _patch_siteverify(monkeypatch, success=False, error_codes=["invalid-input-response"])
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        _reset_outbound()
+        r = client.post(
+            "/auth/otc/request",
+            json={"email": "alice@example.com", "turnstile_token": "fake-bad-token"},
+        )
+        assert r.status_code == 400, r.text
+        # The OTC bcrypt + SMTP path did not run — no envelope was buffered.
+        assert _outbound_otc_envelopes("alice@example.com") == []
+
+
+# ---------------------------------------------------------------------------
+# Missing-token: secret set, no token → 400 + no envelope
+# ---------------------------------------------------------------------------
+
+
+def test_otc_request_refuses_when_turnstile_token_is_missing(app_with_fake_gitea, monkeypatch):
+    from fastapi.testclient import TestClient
+
+    monkeypatch.setenv("CLOUDFLARE_TURNSTILE_SECRET", "test-secret-not-real")
+    monkeypatch.setenv("TURNSTILE_REQUIRED", "true")
+    # Even though we patch httpx.post, the missing-token check fires
+    # before the siteverify call — so the patch is here only as a
+    # safety net in case the implementation regresses to making the
+    # network call anyway.
+    _patch_siteverify(monkeypatch, success=False)
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        _reset_outbound()
+        r = client.post(
+            "/auth/otc/request",
+            json={"email": "alice@example.com"},  # no turnstile_token field at all
+        )
+        assert r.status_code == 400, r.text
+        assert _outbound_otc_envelopes("alice@example.com") == []
+
+
+# ---------------------------------------------------------------------------
+# Missing-secret-soft: no secret, TURNSTILE_REQUIRED=false (default) → admit
+# ---------------------------------------------------------------------------
+
+
+def test_otc_request_admits_when_secret_unset_and_not_required(app_with_fake_gitea, monkeypatch):
+    """v0.12.0 default: the operator has not yet wired the Turnstile
+    secret and has not enabled `TURNSTILE_REQUIRED`. The gate stays
+    open — this is the dev / test / pre-rollout path. Once the
+    operator confirms the secret is in place and flips
+    `TURNSTILE_REQUIRED=true`, missing-secret becomes fail-closed
+    (covered in test_otc_request_refuses_when_required_but_secret_unset).
+    """
+    from fastapi.testclient import TestClient
+
+    monkeypatch.delenv("CLOUDFLARE_TURNSTILE_SECRET", raising=False)
+    monkeypatch.delenv("TURNSTILE_REQUIRED", raising=False)
+    # The httpx.post inside turnstile must not be called in this path —
+    # patch it to a sentinel that explodes if it ever runs.
+    from app import turnstile as turnstile_mod
+
+    def must_not_be_called(*a, **kw):
+        raise AssertionError("siteverify should not run when no secret is configured")
+
+    monkeypatch.setattr(turnstile_mod.httpx, "post", must_not_be_called)
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        _reset_outbound()
+        r = client.post(
+            "/auth/otc/request",
+            json={"email": "alice@example.com"},
+        )
+        assert r.status_code == 200, r.text
+        # The OTC path ran end-to-end — one envelope to the address.
+        assert len(_outbound_otc_envelopes("alice@example.com")) == 1
+
+
+# ---------------------------------------------------------------------------
+# Missing-secret-hard: no secret, TURNSTILE_REQUIRED=true → 500 "misconfigured"
+# ---------------------------------------------------------------------------
+
+
+def test_otc_request_refuses_when_required_but_secret_unset(app_with_fake_gitea, monkeypatch):
+    """Once the operator has flipped `TURNSTILE_REQUIRED=true` to lock
+    down production, a missing secret stops being a soft-fail and
+    becomes a fail-closed 500. This is the regression-detection shape
+    the §20.4 upgrade-steps MAY block calls out — flip the flag once
+    the secret is wired so a future config drift fails loudly instead
+    of silently disabling abuse defense.
+    """
+    from fastapi.testclient import TestClient
+
+    monkeypatch.delenv("CLOUDFLARE_TURNSTILE_SECRET", raising=False)
+    monkeypatch.setenv("TURNSTILE_REQUIRED", "true")
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app) as client:
+        _reset_outbound()
+        r = client.post(
+            "/auth/otc/request",
+            json={"email": "alice@example.com", "turnstile_token": "doesnt-matter"},
+        )
+        assert r.status_code == 500, r.text
+        assert _outbound_otc_envelopes("alice@example.com") == []