Java Security

Hi,
I am trying to integrate my application authentication to a backend system with the ibm websphere form based authentication. Below is the scenario:

1. when the user clicks on a protected url, the container will redirect the user to the login page.
2. instead of displaying the login page, i would like to automatically redirect the user to j_security_check action. which means that instead of displaying the login.jsp page, the user will automatically be redirected to j_security_check to perform some user authentication, and if successful, the application pages will be displayed.

The reason i want to auto redirect the user to j_security_check is because i am implementing some integration work with a backend system. the user will key in the username/password from another system. once the user is authenticated, the user information will be passed to my system. The login page of my system will not be displayed again, and by using the username value, my system will assume that the user has successfully been authenticated (authentication done by the backend system), and therefore automatically gain authorization to login into my application.

i hope that clarifies my problem.
anyone out there has any solution to my problem?
thanks a lot in advance.