New Post: Validating properties with separate validators

class Credentials
{
public string Login { get; protected set; }
public string Password { get; protected set; }
}

and want to implement several validators for login, like, LoginAvailabilityValidator or LoginFormatValidator, what's the correct way to do so?

I need this because in some cases I need to validate Login alone, not as a part of Credentials (could be a bad design, but still, I'm curious).

Implementing AbstractValidator<string> doesn't seem right, I can't even use RuleFor.