The IWriteCookie::put_Item method adds a specified cookie to the write-only Cookie collection.
HRESULT put_Item(
VARIANT key, //VARIANT that contains the name of the cookie
BSTR bstrValue //binary string that contains the cookie value
);
Automation objects can specify that one or more variant parameters are optional. This is done by passing the parameter with the type set to VT_ERROR and a value of DISP_E_PARAMNOTFOUND. If you pass key as an Automation optional parameter, the cookie is treated as a simple cookie and its value is set to bstrValue. Otherwise, the cookie is treated as a dictionary cookie and bstrValue is the value for the cookie's key.