1. Introduction
In the presence of web browser cache, for example, the users can interact not only with the web pages but also with the web browser itself via the use of the special buttons such as Back, Forward, Refresh or via URL rewriting. Such actions of the users may affect the overall navigations of the web pages, which can be quite sensitive to the security of the information they carry. Thus, the behavior of the web browsers may have impact on the correctness of the web applications: a web application providing all correct functionality by itself may however malfunction when it is put into its supporting environment.