public class MyClientCredentials : ClientCredentials
{
    string creditCardNumber;

    public MyClientCredentials()
    {
        // Perform client credentials initialization.
    }

    protected MyClientCredentials(MyClientCredentials other)
        : base(other)
    {
        // Clone fields defined in this class.
        this.creditCardNumber = other.creditCardNumber;
    }

    public string CreditCardNumber
    {
        get
        {
            return this.creditCardNumber;
        }
        set
        {
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }
            this.creditCardNumber = value;
        }
    }

    public override SecurityTokenManager CreateSecurityTokenManager()
    {
        // Return your implementation of the SecurityTokenManager.
        return new MyClientCredentialsSecurityTokenManager(this);
    }

    protected override ClientCredentials CloneCore()
    {
        // Implement the cloning functionality.
        return new MyClientCredentials(this);
    }
}