that return expires_in: 0 ?
also, the expires_in not mentioned in the validate documentation
curl -H "Authorization: OAuth <access token>" https://id.twitch.tv/oauth2/validate
And here is a sample response:
{
"client_id": "<your client ID>",
"login": "<authorized user login>",
"scopes": [
"<requested scopes>"
],
"user_id": "<authorized user ID>"
}