feat(auth): APIKeyAuthBackend resolves token to SA principal (Stage 1 PR2)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/gateway/auth/api_key_backend.py

@@ -11,6 +11,8 @@ from __future__ import annotations
 import logging
 from dataclasses import dataclass
 
+from deerflow.auth.tokens import hash_api_key, split_prefix
+
 logger = logging.getLogger(__name__)
 
 
@@ -30,3 +32,66 @@ def parse_scopes(scopes: str) -> list[str]:
     Empty / whitespace-only segments are dropped.
     """
     return [s.strip() for s in scopes.split(",") if s.strip()]
+
+
+@dataclass(frozen=True)
+class ApiKeyAuthResult:
+    """Everything ``AuthMiddleware`` needs to stamp request state +
+    contextvars from a verified API key."""
+
+    principal: ServicePrincipal
+    workspace_id: str
+    role: str
+    permissions: list[str]
+
+
+class APIKeyAuthBackend:
+    def __init__(self, *, api_key_repo, service_account_repo, workspace_repo) -> None:
+        self._api_key_repo = api_key_repo
+        self._service_account_repo = service_account_repo
+        self._workspace_repo = workspace_repo
+
+    async def authenticate(self, token: str) -> ApiKeyAuthResult | None:
+        """Resolve a plaintext token to an auth result, or None (→ 401)."""
+        # Look up by the indexed public prefix; the repo constant-time
+        # verifies the full hash.
+        key = await self._api_key_repo.get_active_by_hash(hash_api_key(token), key_prefix=split_prefix(token))
+        if key is None:
+            return None
+
+        sa = await self._service_account_repo.get_active(key["service_account_id"])
+        if sa is None:
+            return None
+
+        # SA is not a workspace *member* — bypass the membership filter
+        # with the documented user_id=None admin/migration path.
+        workspace = await self._workspace_repo.get(sa["workspace_id"], user_id=None)
+        if workspace is None or workspace["status"] != "active":
+            return None
+
+        # Best-effort: never block the request if the timestamp write fails.
+        try:
+            await self._api_key_repo.touch_last_used(key["id"])
+        except Exception:  # noqa: BLE001 — best-effort, log and continue
+            logger.warning("touch_last_used failed for api_key %s", key["id"], exc_info=True)
+
+        return ApiKeyAuthResult(
+            principal=ServicePrincipal(id=sa["id"]),
+            workspace_id=sa["workspace_id"],
+            role=sa["role"],
+            permissions=parse_scopes(key["scopes"]),
+        )
+
+
+def build_api_key_backend() -> APIKeyAuthBackend | None:
+    """Construct a backend from the global session factory, or None when
+    persistence is the in-memory backend (no DB → no API keys)."""
+    from deerflow.persistence.api_key import ApiKeyRepository
+    from deerflow.persistence.engine import get_session_factory
+    from deerflow.persistence.service_account import ServiceAccountRepository
+    from deerflow.persistence.workspace import WorkspaceRepository
+
+    sf = get_session_factory()
+    if sf is None:
+        return None
+    return APIKeyAuthBackend(api_key_repo=ApiKeyRepository(sf), service_account_repo=ServiceAccountRepository(sf), workspace_repo=WorkspaceRepository(sf))