In order to obtain Cookies object call WebDriver.Cookies.

var cookies = WebDriver.Cookies();

With this object you can read, create and delete cookies.

// Print names of all cookies
var cs = cookies.AllCookies();
for(var i = 0; i < cs.length; i++)
    // cs[i] contains Cookie object

// Get cookie by name, returns Cookie object
var c = cookies.GetCookieNamed("SESSION");

// Create new cookie
cookies.AddCookie({Name: "MySimpleCookie", Value: "MyValue"});

// Create new cookie for given domain and path
cookies.AddCookie({Name: "MyComplexCookie", Value: "MyValue", Domain: "", Path: "/"});

// Create cookie with expiration
var dt = new Date(); // Construct date-time string in the format "2018-12-30T13:15:00-05:00"
var expDate = UtilGetPaddedZeroesDate(dt) + "T" + UtilGetPaddedZeroesTime(dt) + "-05:00";
cookies.AddCookie({Name: "MyExpiringCookie", Value: "MyValue", Domain: "", Path: "/", Expiry: expDate});

// Delete cookies
cookies.DeleteCookie({Name: "MySimpleCookie", Value: "MyValue"});

Cookie object in JavaScript has following structure:

    Name: "CookieName",
    Value: "CookieValue",
    Domain: "",
    Path: "/",
    Expiry: "2018-12-28T13:15.00-05:00"

Cookies class is described in Rapise help file.

Check out the sample test on GitHub.