The present invention provides a security module for Web application, especially a portal application, using a rewriter proxy. The security module ensures that the rewritten URIs are appended by an authentication identifier for determining whether the rewritten URI has not been changed. Preferably, the authentication identifier can be generated by applying a secure hash algorithm and/or secret key to the original URIs of the remote resource or the entire rewritten URIs. When a client activates those URIs, a request is sent to the rewriter proxy. Before a connection to the access protected remote resource is established, the security module validates whether the URIs contained in the user client request have been changed by the user.