ASP.NET Enable Session in Web Service Methods

Ever tried accessing session variables in Web Service methods? It won't work unless you add a little property in the WebMethod header of the functions.

For example, the basic hello world:

[WebMethod(EnableSession=true)]
public void HelloWorld()
{
    ...
}

Just add the statement EnableSession=true and you'll be able to access session variables found normally in aspx pages like the following sample.

string userid = Session["userid"].ToString();