Grant mobile plans from verified App Store and Play purchases (#78) (#79)

## Summary
- Mobile access is granted by `POST /api/finance/store/confirm/` after the app finishes a StoreKit or Play Billing purchase.
- App Store signed transactions are checked against Apple Root CA G3. Play purchase tokens are checked with the Play Developer API.
- The RevenueCat webhook no longer grants a plan. Stripe Checkout and the Stripe webhook stay for the website.
- A purchase account token must match the signed-in user, and a transaction already linked to another account is rejected. Access ends when the verified period end passes unless the app confirms again.

Client: ai_ml_operations/chat_web_app#122

## Config
- `APPLE_IAP_BUNDLE_ID` (default `ai.hesychia.chat`)
- `GOOGLE_PLAY_PACKAGE_NAME`
- `GOOGLE_PLAY_SERVICE_ACCOUNT_JSON` (JSON or a file path)
- Plan `revenuecat_product_id` or `REVENUECAT_PRODUCT_PLAN_MAP` maps the store product to a plan

## Test plan
- [x] `python manage.py test monetization.tests.test_store_purchases monetization.tests.test_revenuecat monetization.tests.test_plans_quotas`
- [ ] Confirm an App Store sandbox transaction and a Play license-test purchase against a configured backend
- [ ] Confirm a token already linked to another user is rejected
- [ ] Confirm `GET /subscription/` returns `store_account_token` and flips a lapsed store sub to canceled

Reviewed-on: #79

llm_be/monetization/services/plans.py

@@ -247,6 +247,8 @@ def needs_checkout(user) -> bool:
         UserSubscription.Source.ADMIN,
         UserSubscription.Source.STRIPE,
         UserSubscription.Source.REVENUECAT,
+        UserSubscription.Source.APP_STORE,
+        UserSubscription.Source.PLAY_STORE,
     ):
         return False
     return True
@@ -457,8 +459,9 @@ def assign_plan_from_revenuecat(
     cancel_at_period_end: bool | None = None,
     current_period_end=None,
     keep_existing_plan_if_unknown: bool = False,
+    source: str | None = None,
 ) -> UserSubscription:
-    """Assign a catalog plan from a RevenueCat store purchase event."""
+    """Assign a catalog plan from a verified store purchase."""
     seed_subscription_plans(update_existing=False)
     existing = (
         UserSubscription.objects.filter(user=user).select_related("plan").first()
@@ -493,7 +496,7 @@ def assign_plan_from_revenuecat(
     sub = assign_plan(
         user,
         plan=plan,
-        source=UserSubscription.Source.REVENUECAT,
+        source=source or UserSubscription.Source.REVENUECAT,
         status=status,
         revenuecat_original_transaction_id=revenuecat_original_transaction_id or "",
         log_auth_event=False,

llm_be/monetization/services/store_purchases.py

@@ -0,0 +1,617 @@
+"""Verify App Store and Play Store purchases and grant entitlements.
+
+The mobile app completes the purchase with StoreKit or Play Billing, then
+POSTs the signed transaction or purchase token. This module checks that
+payload with Apple or Google and writes the subscription ledger. Store
+webhooks are not accepted.
+"""
+
+from __future__ import annotations
+
+import base64
+import json
+import logging
+import time
+import uuid
+from dataclasses import dataclass
+from datetime import datetime, timezone as dt_timezone
+from pathlib import Path
+from typing import Any
+from urllib.parse import quote
+
+import jwt
+import requests
+from cryptography import x509
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric import ec, padding
+from django.conf import settings
+from django.db import transaction
+from django.utils import timezone
+
+from monetization.models import Invoice, Payment, UserSubscription
+from monetization.services.plans import (
+    assign_plan_from_revenuecat,
+    log_subscription_auth_event,
+    resolve_plan_from_revenuecat_product,
+)
+
+logger = logging.getLogger(__name__)
+
+# uuid5(NAMESPACE_URL, this name). Do not change; clients receive the result.
+_STORE_ACCOUNT_NAMESPACE = uuid.uuid5(
+    uuid.NAMESPACE_URL,
+    "https://chat.aimloperations.com/store-account",
+)
+_APP_STORE_CERT_OID = x509.ObjectIdentifier("1.2.840.113635.100.6.11.1")
+_PLAY_SCOPE = "https://www.googleapis.com/auth/androidpublisher"
+_BUNDLED_APPLE_ROOT = (
+    Path(__file__).resolve().parent.parent / "certs" / "apple_root_g3.pem"
+)
+
+_STORE_SOURCES = frozenset(
+    {
+        UserSubscription.Source.APP_STORE,
+        UserSubscription.Source.PLAY_STORE,
+        UserSubscription.Source.REVENUECAT,
+    }
+)
+
+
+class StoreNotConfiguredError(Exception):
+    """Apple or Google credentials required to verify a purchase are missing."""
+
+
+class StorePurchaseRejected(Exception):
+    """The store payload is not an active purchase for this user."""
+
+
+class StoreVerificationError(Exception):
+    """The store API could not be reached."""
+
+
+@dataclass(frozen=True)
+class VerifiedStorePurchase:
+    source: str
+    store_label: str
+    product_id: str
+    transaction_id: str
+    original_transaction_id: str
+    expires_at: datetime | None
+    purchased_at: datetime | None
+    cancel_at_period_end: bool
+    status: str
+    price_cents: int
+    currency: str
+    account_token: str
+
+
+def store_account_token(user_id: int) -> str:
+    """Stable store account id for this user. Pass it to StoreKit and Play."""
+    return str(uuid.uuid5(_STORE_ACCOUNT_NAMESPACE, str(user_id)))
+
+
+def expire_lapsed_store_subscription(sub: UserSubscription | None):
+    """End store access once the verified period has passed.
+
+    Renewals arrive when the app confirms the store entitlement again.
+    """
+    if sub is None or sub.source not in _STORE_SOURCES:
+        return sub
+    if sub.status != UserSubscription.Status.ACTIVE or not sub.current_period_end:
+        return sub
+    if sub.current_period_end > timezone.now():
+        return sub
+    prev_status = sub.status
+    sub.status = UserSubscription.Status.CANCELED
+    sub.cancel_at_period_end = False
+    sub.save(update_fields=["status", "cancel_at_period_end", "last_modified"])
+    if prev_status != UserSubscription.Status.CANCELED:
+        log_subscription_auth_event(
+            sub.user,
+            started=False,
+            detail=(
+                f"plan={sub.plan.slug if sub.plan_id else 'none'} "
+                f"source={sub.source} status={sub.status} "
+                "reason=store_period_ended"
+            ),
+        )
+    return sub
+
+
+def confirm_store_purchase(user, payload: dict[str, Any]) -> UserSubscription:
+    """Verify one store purchase for the authenticated user and grant it."""
+    store = (payload.get("store") or "").strip().lower()
+    product_id = (payload.get("product_id") or "").strip()
+    if store == UserSubscription.Source.APP_STORE:
+        verified = verify_apple_signed_transaction(
+            signed_transaction=(payload.get("signed_transaction") or "").strip(),
+            product_id=product_id,
+            transaction_id=(payload.get("transaction_id") or "").strip(),
+        )
+    elif store == UserSubscription.Source.PLAY_STORE:
+        verified = verify_google_subscription(
+            product_id=product_id,
+            purchase_token=(payload.get("purchase_token") or "").strip(),
+            transaction_id=(payload.get("transaction_id") or "").strip(),
+        )
+    else:
+        raise StorePurchaseRejected("store must be app_store or play_store.")
+    if verified.product_id != product_id:
+        raise StorePurchaseRejected("Store product does not match this purchase.")
+    return grant_verified_store_purchase(user, verified)
+
+
+def verify_apple_signed_transaction(
+    *,
+    signed_transaction: str,
+    product_id: str,
+    transaction_id: str = "",
+) -> VerifiedStorePurchase:
+    """Verify a StoreKit 2 signed transaction against Apple's root."""
+    if not signed_transaction:
+        raise StorePurchaseRejected("App Store purchases require signed_transaction.")
+    bundle_id = (getattr(settings, "APPLE_IAP_BUNDLE_ID", "") or "").strip()
+    if not bundle_id:
+        raise StoreNotConfiguredError("APPLE_IAP_BUNDLE_ID is not configured.")
+    roots = _load_apple_roots()
+    if not roots:
+        raise StoreNotConfiguredError("No Apple root certificate is configured.")
+
+    try:
+        header = jwt.get_unverified_header(signed_transaction)
+    except jwt.PyJWTError as exc:
+        raise StorePurchaseRejected("Invalid App Store signed transaction.") from exc
+    x5c = header.get("x5c") if isinstance(header, dict) else None
+    if not isinstance(x5c, list) or not x5c:
+        raise StorePurchaseRejected("App Store transaction is missing its certificate.")
+    try:
+        certs = [_load_der_cert(item) for item in x5c]
+        leaf = _trusted_leaf(certs, roots)
+    except StorePurchaseRejected:
+        raise
+    except Exception as exc:
+        raise StorePurchaseRejected("App Store certificate chain is not trusted.") from exc
+    _require_app_store_oid(leaf)
+
+    try:
+        claims = jwt.decode(
+            signed_transaction,
+            leaf.public_key(),
+            algorithms=["ES256"],
+            options={"verify_aud": False, "verify_exp": False},
+        )
+    except jwt.PyJWTError as exc:
+        raise StorePurchaseRejected("App Store transaction signature is invalid.") from exc
+    if not isinstance(claims, dict):
+        raise StorePurchaseRejected("App Store transaction payload is invalid.")
+
+    claim_bundle = str(claims.get("bundleId") or "")
+    if claim_bundle != bundle_id:
+        raise StorePurchaseRejected("App Store bundle id does not match this app.")
+    claim_product = str(claims.get("productId") or "")
+    if product_id and claim_product != product_id:
+        raise StorePurchaseRejected("App Store product does not match this purchase.")
+    claim_txn = str(claims.get("transactionId") or "")
+    if transaction_id and claim_txn and transaction_id != claim_txn:
+        raise StorePurchaseRejected("App Store transaction id does not match.")
+    if not claim_txn:
+        raise StorePurchaseRejected("App Store transaction id is missing.")
+
+    expires_at = _ms_to_dt(claims.get("expiresDate"))
+    purchased_at = _ms_to_dt(claims.get("purchaseDate"))
+    revoked = _ms_to_dt(claims.get("revocationDate")) is not None
+    now = timezone.now()
+    if revoked or (expires_at is not None and expires_at <= now):
+        status = UserSubscription.Status.CANCELED
+    else:
+        status = UserSubscription.Status.ACTIVE
+
+    price_cents = 0
+    raw_price = claims.get("price")
+    try:
+        if raw_price is not None:
+            price_cents = max(0, int(raw_price) // 10)
+    except (TypeError, ValueError):
+        price_cents = 0
+    currency = str(claims.get("currency") or "usd").lower()
+    original = str(claims.get("originalTransactionId") or claim_txn)
+    return VerifiedStorePurchase(
+        source=UserSubscription.Source.APP_STORE,
+        store_label="APP_STORE",
+        product_id=claim_product,
+        transaction_id=claim_txn,
+        original_transaction_id=original,
+        expires_at=expires_at,
+        purchased_at=purchased_at,
+        cancel_at_period_end=False,
+        status=status,
+        price_cents=price_cents,
+        currency=currency,
+        account_token=str(claims.get("appAccountToken") or ""),
+    )
+
+
+def verify_google_subscription(
+    *,
+    product_id: str,
+    purchase_token: str,
+    transaction_id: str = "",
+) -> VerifiedStorePurchase:
+    """Verify a Play Billing purchase token with the Android Publisher API."""
+    if not purchase_token:
+        raise StorePurchaseRejected("Play Store purchases require purchase_token.")
+    if not product_id:
+        raise StorePurchaseRejected("Play Store purchases require product_id.")
+    body = fetch_google_subscription(purchase_token)
+    return _verified_from_google(
+        body,
+        product_id=product_id,
+        purchase_token=purchase_token,
+        transaction_id=transaction_id,
+    )
+
+
+def fetch_google_subscription(purchase_token: str) -> dict[str, Any]:
+    """GET purchases.subscriptionsv2 for this token. Tests patch this."""
+    package_name = (getattr(settings, "GOOGLE_PLAY_PACKAGE_NAME", "") or "").strip()
+    raw = (getattr(settings, "GOOGLE_PLAY_SERVICE_ACCOUNT_JSON", "") or "").strip()
+    if not package_name or not raw:
+        raise StoreNotConfiguredError(
+            "Google Play verification is not configured "
+            "(GOOGLE_PLAY_PACKAGE_NAME and GOOGLE_PLAY_SERVICE_ACCOUNT_JSON)."
+        )
+    info = _load_service_account_info(raw)
+    try:
+        access_token = _google_access_token(info)
+        url = (
+            "https://androidpublisher.googleapis.com/androidpublisher/v3/"
+            f"applications/{quote(package_name, safe='')}/purchases/"
+            f"subscriptionsv2/tokens/{quote(purchase_token, safe='')}"
+        )
+        response = requests.get(
+            url,
+            headers={"Authorization": f"Bearer {access_token}"},
+            timeout=15,
+        )
+    except (requests.RequestException, ValueError, OSError) as exc:
+        logger.exception("Play Store verification request failed")
+        raise StoreVerificationError("Play Store verification failed.") from exc
+    if response.status_code == 404:
+        raise StorePurchaseRejected("Play Store purchase was not found.")
+    if response.status_code >= 400:
+        logger.error(
+            "Play Store verification HTTP %s",
+            response.status_code,
+        )
+        if response.status_code >= 500:
+            raise StoreVerificationError("Play Store verification failed.")
+        raise StorePurchaseRejected("Play Store rejected this purchase token.")
+    try:
+        body = response.json()
+    except ValueError as exc:
+        raise StoreVerificationError("Play Store returned an invalid response.") from exc
+    if not isinstance(body, dict):
+        raise StoreVerificationError("Play Store returned an invalid response.")
+    return body
+
+
+def _verified_from_google(
+    body: dict[str, Any],
+    *,
+    product_id: str,
+    purchase_token: str,
+    transaction_id: str,
+) -> VerifiedStorePurchase:
+    line_items = body.get("lineItems") or []
+    match = None
+    if isinstance(line_items, list):
+        for item in line_items:
+            if isinstance(item, dict) and str(item.get("productId") or "") == product_id:
+                match = item
+                break
+    if match is None:
+        raise StorePurchaseRejected("Play Store product does not match this purchase.")
+
+    state = str(body.get("subscriptionState") or "")
+    expires_at = _parse_rfc3339(match.get("expiryTime"))
+    now = timezone.now()
+    expired = expires_at is not None and expires_at <= now
+    cancel_at_period_end = False
+    if state in {"SUBSCRIPTION_STATE_PENDING", "SUBSCRIPTION_STATE_PENDING_PURCHASE_CANCELED"}:
+        raise StorePurchaseRejected("Play Store purchase is still pending.")
+    if state in {"SUBSCRIPTION_STATE_ACTIVE", "SUBSCRIPTION_STATE_IN_GRACE_PERIOD"} and not expired:
+        status = UserSubscription.Status.ACTIVE
+    elif state == "SUBSCRIPTION_STATE_CANCELED" and not expired:
+        status = UserSubscription.Status.ACTIVE
+        cancel_at_period_end = True
+    elif state == "SUBSCRIPTION_STATE_ON_HOLD":
+        status = UserSubscription.Status.PAST_DUE
+    else:
+        status = UserSubscription.Status.CANCELED
+
+    auto_renew = (match.get("autoRenewingPlan") or {}) if isinstance(match, dict) else {}
+    if isinstance(auto_renew, dict) and auto_renew.get("autoRenewEnabled") is False and not expired:
+        if status == UserSubscription.Status.ACTIVE:
+            cancel_at_period_end = True
+
+    order_id = str(match.get("latestSuccessfulOrderId") or transaction_id or purchase_token)
+    identifiers = body.get("externalAccountIdentifiers") or {}
+    account_token = ""
+    if isinstance(identifiers, dict):
+        account_token = str(identifiers.get("obfuscatedExternalAccountId") or "")
+    price_cents, currency = _google_price(auto_renew if isinstance(auto_renew, dict) else {})
+    return VerifiedStorePurchase(
+        source=UserSubscription.Source.PLAY_STORE,
+        store_label="PLAY_STORE",
+        product_id=product_id,
+        transaction_id=order_id,
+        original_transaction_id=purchase_token,
+        expires_at=expires_at,
+        purchased_at=None,
+        cancel_at_period_end=cancel_at_period_end,
+        status=status,
+        price_cents=price_cents,
+        currency=currency,
+        account_token=account_token,
+    )
+
+
+@transaction.atomic
+def grant_verified_store_purchase(user, verified: VerifiedStorePurchase) -> UserSubscription:
+    plan = resolve_plan_from_revenuecat_product(verified.product_id)
+    if plan is None:
+        raise StorePurchaseRejected("This store product is not mapped to a plan.")
+
+    expected = store_account_token(user.pk)
+    if verified.account_token and verified.account_token.lower() != expected.lower():
+        raise StorePurchaseRejected("Purchase account token does not match this user.")
+
+    original = verified.original_transaction_id
+    if original:
+        taken = (
+            UserSubscription.objects.select_for_update()
+            .filter(revenuecat_original_transaction_id=original)
+            .exclude(user=user)
+            .exists()
+        )
+        if taken:
+            raise StorePurchaseRejected(
+                "This purchase is already linked to another account."
+            )
+
+    sub = assign_plan_from_revenuecat(
+        user,
+        plan_slug=plan.slug,
+        product_id=verified.product_id,
+        revenuecat_original_transaction_id=original,
+        status=verified.status,
+        cancel_at_period_end=verified.cancel_at_period_end,
+        current_period_end=verified.expires_at,
+        keep_existing_plan_if_unknown=False,
+        source=verified.source,
+    )
+
+    if verified.status != UserSubscription.Status.ACTIVE:
+        return sub
+
+    amount = verified.price_cents or plan.price_cents
+    currency = (verified.currency or plan.currency or "usd").lower()
+    event_id = f"{verified.source}:{verified.transaction_id}"
+    invoice, _created = Invoice.objects.update_or_create(
+        revenuecat_event_id=event_id,
+        defaults={
+            "user": user,
+            "company": getattr(user, "company", None),
+            "provider": verified.source,
+            "status": Invoice.Status.PAID,
+            "currency": currency,
+            "amount_due": amount,
+            "amount_paid": amount,
+            "period_start": verified.purchased_at,
+            "period_end": verified.expires_at,
+            "revenuecat_store": verified.store_label,
+            "description": f"{plan.name} — {verified.store_label}",
+            "hosted_invoice_url": "",
+        },
+    )
+    Payment.objects.update_or_create(
+        revenuecat_transaction_id=verified.transaction_id,
+        defaults={
+            "user": user,
+            "company": getattr(user, "company", None),
+            "invoice": invoice,
+            "provider": verified.source,
+            "status": Payment.Status.SUCCEEDED,
+            "currency": currency,
+            "amount": amount,
+            "paid_at": verified.purchased_at or timezone.now(),
+            "failure_message": "",
+        },
+    )
+    return sub
+
+
+def _load_apple_roots() -> list[x509.Certificate]:
+    pems: list[str] = []
+    extra = (getattr(settings, "APPLE_IAP_ROOT_PEM", "") or "").strip()
+    if extra:
+        pems.append(extra)
+    if _BUNDLED_APPLE_ROOT.is_file():
+        pems.append(_BUNDLED_APPLE_ROOT.read_text(encoding="utf-8"))
+    roots: list[x509.Certificate] = []
+    for pem in pems:
+        try:
+            roots.append(x509.load_pem_x509_certificate(pem.encode("utf-8")))
+        except ValueError:
+            logger.error("Ignoring an unreadable Apple root certificate")
+    return roots
+
+
+def _load_der_cert(value: Any) -> x509.Certificate:
+    if not isinstance(value, str) or not value.strip():
+        raise StorePurchaseRejected("App Store certificate is missing.")
+    try:
+        der = base64.b64decode(value)
+        return x509.load_der_x509_certificate(der)
+    except (ValueError, TypeError) as exc:
+        raise StorePurchaseRejected("App Store certificate is invalid.") from exc
+
+
+def _trusted_leaf(
+    certs: list[x509.Certificate],
+    roots: list[x509.Certificate],
+) -> x509.Certificate:
+    if not certs:
+        raise StorePurchaseRejected("App Store certificate chain is empty.")
+    now = datetime.now(dt_timezone.utc)
+    for cert in certs:
+        if cert.not_valid_before_utc > now or cert.not_valid_after_utc < now:
+            raise StorePurchaseRejected("App Store certificate is not currently valid.")
+    for index in range(len(certs) - 1):
+        _verify_signed_by(certs[index], certs[index + 1])
+        if certs[index].issuer != certs[index + 1].subject:
+            raise StorePurchaseRejected("App Store certificate issuer mismatch.")
+    last = certs[-1]
+    root_fps = {root.fingerprint(hashes.SHA256()) for root in roots}
+    if last.fingerprint(hashes.SHA256()) in root_fps:
+        return certs[0]
+    for root in roots:
+        try:
+            _verify_signed_by(last, root)
+        except Exception:
+            continue
+        if last.issuer == root.subject:
+            return certs[0]
+    raise StorePurchaseRejected("App Store certificate chain is not trusted.")
+
+
+def _verify_signed_by(child: x509.Certificate, issuer: x509.Certificate) -> None:
+    public_key = issuer.public_key()
+    signature_hash = child.signature_hash_algorithm
+    if signature_hash is None:
+        raise StorePurchaseRejected("App Store certificate has no signature hash.")
+    if isinstance(public_key, ec.EllipticCurvePublicKey):
+        public_key.verify(
+            child.signature,
+            child.tbs_certificate_bytes,
+            ec.ECDSA(signature_hash),
+        )
+        return
+    public_key.verify(
+        child.signature,
+        child.tbs_certificate_bytes,
+        padding.PKCS1v15(),
+        signature_hash,
+    )
+
+
+def _require_app_store_oid(leaf: x509.Certificate) -> None:
+    try:
+        leaf.extensions.get_extension_for_oid(_APP_STORE_CERT_OID)
+    except x509.ExtensionNotFound as exc:
+        raise StorePurchaseRejected(
+            "Signed transaction certificate is not an App Store certificate."
+        ) from exc
+
+
+def _google_access_token(info: dict[str, Any]) -> str:
+    """OAuth JWT bearer grant for a Play Console service account."""
+    client_email = info.get("client_email")
+    private_key = info.get("private_key")
+    token_uri = info.get("token_uri") or "https://oauth2.googleapis.com/token"
+    if not client_email or not private_key:
+        raise StoreNotConfiguredError(
+            "GOOGLE_PLAY_SERVICE_ACCOUNT_JSON is missing client_email or private_key."
+        )
+    now = int(time.time())
+    assertion = jwt.encode(
+        {
+            "iss": client_email,
+            "scope": _PLAY_SCOPE,
+            "aud": token_uri,
+            "iat": now,
+            "exp": now + 3600,
+        },
+        private_key,
+        algorithm="RS256",
+    )
+    try:
+        response = requests.post(
+            token_uri,
+            data={
+                "grant_type": "urn:ietf:params:oauth:grant-type:jwt-bearer",
+                "assertion": assertion,
+            },
+            timeout=15,
+        )
+    except requests.RequestException as exc:
+        raise StoreVerificationError("Play Store verification failed.") from exc
+    if response.status_code >= 400:
+        raise StoreVerificationError("Play Store authentication failed.")
+    try:
+        token = response.json().get("access_token")
+    except ValueError as exc:
+        raise StoreVerificationError("Play Store authentication failed.") from exc
+    if not token:
+        raise StoreVerificationError("Play Store authentication failed.")
+    return str(token)
+
+
+def _load_service_account_info(raw: str) -> dict[str, Any]:
+    text = raw
+    if not raw.lstrip().startswith("{"):
+        path = Path(raw)
+        if path.is_file():
+            text = path.read_text(encoding="utf-8")
+    try:
+        info = json.loads(text)
+    except json.JSONDecodeError as exc:
+        raise StoreNotConfiguredError(
+            "GOOGLE_PLAY_SERVICE_ACCOUNT_JSON is not valid JSON."
+        ) from exc
+    if not isinstance(info, dict):
+        raise StoreNotConfiguredError(
+            "GOOGLE_PLAY_SERVICE_ACCOUNT_JSON must be a JSON object."
+        )
+    return info
+
+
+def _ms_to_dt(value: Any) -> datetime | None:
+    if value is None or value == "":
+        return None
+    try:
+        ms = int(value)
+    except (TypeError, ValueError):
+        return None
+    if ms <= 0:
+        return None
+    return datetime.fromtimestamp(ms / 1000.0, tz=dt_timezone.utc)
+
+
+def _parse_rfc3339(value: Any) -> datetime | None:
+    if not value or not isinstance(value, str):
+        return None
+    try:
+        parsed = datetime.fromisoformat(value.replace("Z", "+00:00"))
+    except ValueError:
+        return None
+    if parsed.tzinfo is None:
+        return parsed.replace(tzinfo=dt_timezone.utc)
+    return parsed
+
+
+def _google_price(auto_renew: dict[str, Any]) -> tuple[int, str]:
+    price = auto_renew.get("recurringPrice") if isinstance(auto_renew, dict) else None
+    if not isinstance(price, dict):
+        return 0, "usd"
+    currency = str(price.get("currencyCode") or "usd").lower()
+    try:
+        units = int(price.get("units") or 0)
+    except (TypeError, ValueError):
+        units = 0
+    try:
+        nanos = int(price.get("nanos") or 0)
+    except (TypeError, ValueError):
+        nanos = 0
+    cents = units * 100 + nanos // 10_000_000
+    return max(0, cents), currency