isOAuthTokenExpired function
Check if an OAuth token is expired (with 5 minute buffer).
Implementation
bool isOAuthTokenExpired(int? expiresAt) {
if (expiresAt == null) return false;
const bufferTime = 5 * 60 * 1000; // 5 minutes in ms
final now = DateTime.now().millisecondsSinceEpoch;
return (now + bufferTime) >= expiresAt;
}