Read a Javascript cookie-value from a .NET codebehind

In my part of the web page I have put a value in a Javascript cookie like this:

function SkrivJSCookie() {
         document.cookie = "test_cookie=Test99";
         }

In my codebehind (VB), I want to have the value of the cookie (‘Test99’) transferred to a textbox (Textbox1) when a button is clicked.

From a large Google search it seems, that the solution may be to use ‘HttpServletRequest’ in some way, but I cannot make it work at all.

It seems like a pretty simple issue but how can this be accomplished?

Thank you in advance!