willExpireSoon method
Returns true if the token will expire within threshold.
Implementation
bool willExpireSoon({Duration threshold = const Duration(minutes: 5)}) {
if (_currentToken == null || _currentToken!.expiresIn == null) return true;
final expiresAt = _currentToken!.issuedAt.add(
Duration(seconds: _currentToken!.expiresIn!),
);
final now = DateTime.now();
return expiresAt.difference(now) <= threshold;
}