SEC-1660: Updated FAQ to explain that session-fixation protection may cause problems if switching between HTTP and HTTPS, and also updated information to advise against switching in the first place.

docs/faq/src/docbook/faq.xml

@@ -247,9 +247,18 @@
                         switching back to HTTP afterwards. It doesn't work - I just end up back at
                         the login page after authenticating. </para></question>
                 <answer><para> This happens because sessions created under HTTPS, for which the session cookie is marked as
-                        <quote>secure</quote>, cannot subsequently be used under HTTP. The browser will not send the cookie
-                        back to the server and any session state will be lost (including the security context information).
-                        Starting a session in HTTP first should work as the session cookie won't be marked as secure.</para></answer>
+                                <quote>secure</quote>, cannot subsequently be used under HTTP. The
+                            browser will not send the cookie back to the server and any session
+                            state will be lost (including the security context information).
+                            Starting a session in HTTP first should work as the session cookie won't
+                            be marked as secure (you will also have to disable Spring Security's
+                            <link xlink:href="http://static.springsource.org/spring-security/site/docs/3.1.x/reference/springsecurity-single.html#ns-session-fixation">
+                            Session Fixation Protection</link> support to prevent it from creating a new secure session.
+                            Note that this is not a good idea in general, as any application which uses HTTP at all is vulnerable to
+                            man-in-the-middle attacks. To be truly secure, the user should begin accessing your site in HTTPS and continue
+                            using it until they log out. Even clicking on an HTTPS link from a page accessed over HTTP is potentially risky.
+                            If you need more convincing, check out a tool like <link xlink:href="http://www.thoughtcrime.org/software/sslstrip/">sslstrip</link>.
+                            </para></answer>
             </qandaentry>
 
             <qandaentry>