Logout via HttpModule

I have derived an HttpModule, and I would like to log the current user out upon certain conditions.I have this "working", though I am not sure that it is 100% proper (or complete). Here is the basiccode I have used, followed by a few comments and questions:
 ----------------------------------------------------------------------------------------- public void Init(HttpApplication app)
{
app.PostAuthenticateRequest += new EventHandler(OnPostAuthenticateRequest);
}

void OnPostAuthenticateRequest(object sender, EventArgs e)
{
HttpApplication app = (HttpApplication)sender;
HttpContext context = app.Context;

str ...