SEC-1544: Added CookieClearingLogoutHandler and 'delete-cookies' attribute to the 'logout' namespace element.

When the user logs out, the handler will attempt to delete the named cookies (which it is constructor-injected with) by expiring them in the response.

Also added documentation on the feature and a suggestion for deleting JSESSIONID through an Apache proxy server, if the servlet container doesn't allow clearing the session cookie.

web/src/test/java/org/springframework/security/web/authentication/logout/CookieClearingLogoutHandlerTests.java

@@ -1,7 +1,30 @@
 package org.springframework.security.web.authentication.logout;
 
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.mock;
+
+import javax.servlet.http.Cookie;
+
+import org.junit.Test;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.security.core.Authentication;
+
 /**
  * @author Luke Taylor
  */
 public class CookieClearingLogoutHandlerTests {
+    @Test
+    public void configuredCookiesAreCleared() {
+        MockHttpServletResponse response = new MockHttpServletResponse();
+        MockHttpServletRequest request = new MockHttpServletRequest();
+        request.setContextPath("/app");
+        CookieClearingLogoutHandler handler = new CookieClearingLogoutHandler("my_cookie", "my_cookie_too");
+        handler.logout(request, response, mock(Authentication.class));
+        assertEquals(2, response.getCookies().length);
+        for (Cookie c : response.getCookies()) {
+            assertEquals("/app", c.getPath());
+            assertEquals(0, c.getMaxAge());
+        }
+    }
 }