curl --request GET \
  --url https://app.autoposting.ai/api-proxy/kbs/{kbId}/docs/{docId}/file-access \
  --header 'Authorization: Bearer <token>'

{
  "success": true,
  "data": {
    "url": "https://storage.autoposting.ai/docs/doc_01HXYZ.pdf?signature=...",
    "expiresAt": "2024-01-01T01:00:00Z"
  }
}