WKWebView clear all cookies

The WKWebView needs some means to clear all cookies and the session cache.

I am using WKWebView combined with the Google Identity Toolkit to perform user authentication. I user cannot completely sign out if there is no means to clear all cached cookies. I can remove the authentication token that is used by my application to access my site. However when the user signs back in, via the google identity toolkit, they do not need to enter a password. This is the behaviour one expects if running in a standard desktop browser where the login is shared by several web sites. It is not the behaviour one expects in application. The way to totally and completely logout in a desktop scenario is to manually clear the browser cache. The way to accomplish the same in the an application is for the application to clear the cache - or at least the cached cookies.