public interface IToken { bool IsExpired(); bool IsValid(); // Other token-related methods } public class UserToken : IToken { private DateTime expirationTime; public UserToken(DateTime expiry) { expirationTime = expiry; } public bool IsExpired() { return DateTime.Now > expirationTime; } public bool IsValid() { return !IsExpired(); } }In this example, we define an IToken interface that specifies two methods, IsExpired() and IsValid(). We then create a UserToken class that implements the interface and provides an implementation for each of the methods. The package library that contains IToken and other related security classes and interfaces might be called something like "Security" or "Authentication."