Question

I have MVC application configured to use Forms Authentication. I’m signing out users by calling LogOff action

 public ActionResult LogOff()
    {
        FormsAuthentication.SignOut();

        DropUserInfo();

        return RedirectToUrl(null, "Home", "Index", null);
    }

But everytime code reaches to FormsAuthentication.SingOut() line, applications throws an exception

Server cannot modify cookies after HTTP headers have been sent

What error message says is pretty clear, thou I can’t understand, how is that possible that Http headers have been sent while calling FormsAuthentication.SingOut() method.

So the question is what causes the error, and how to solve this ?

Answer 1

I’ve initiated Redirect() method call, before calling LogOff() function in ActionFilter, which cased the error to be thrown.

Hope this will help someone else.