title: Spring Security Pre-Authentication / Login
body: <p>I did a proof of concept with Spring Security in order to perform pre authentication by using the PRE_AUTH_FILTER filter. It worked OK, but I'd like to know if I can redirect to the login page if the this filter does not work, because I get HTTP 403.<br>
  I mean, if the initial request does not contain the SM_USER field in the header, how can I redirect to the login page? I need to consider these two scenarios (when it contains the field - SM_USER -, and when not) and I was not able to get it working. Any ideas about it? </p>