The IWriteCookie::put_Secure method sets the Secure attribute of the write-only Cookies collection to the specified value.
HRESULT put_Secure(
VARIANT_BOOL fSecure // contains the new value for the Secure attribute
);
You can use this method to specify that a cookie is secure. If you set this value to TRUE, a Secure flag will be added to the Set-Cookie header sent to the client. The Secure flag instructs the client to use only secure means to access the server when sending back the cookie.