When writing your own HTTP Module you will need to have an exclusion list, so that not all HTTP request are intercepted by this module. Like for example: HTTP requests for CSS, JS, Images and even Html templates.

Here is what I used in one of our recent projects

private bool ShouldProcessRequestForSignUp(HttpRequest request)
{
    bool isAnAjaxRequest = request.RequestContext.HttpContext.Request.IsAjaxRequest();
    bool isRequestIsForLogoff = request.Url.AbsolutePath.ToLower().Contains("/account/logoff");
    bool isRequestIsForLogin = request.Url.AbsolutePath.ToLower().Contains("/account/login");
    bool isRequestForResources = (request.Url.AbsolutePath.ToLower().Contains("content") || request.Url.AbsolutePath.ToLower().Contains("scripts"));
    if (isAnAjaxRequest)
        return false;
    if (isRequestFortheSignupPage || isRequestIsForLogoff || isRequestIsForLogin)
        return false;
    if (isRequestForResources)
        return false;
    return true;
}