Polish CSRF log in caveat with link

docs/manual/src/asciidoc/index.adoc

@@ -3051,7 +3051,7 @@ Alternatively, specifying a custom `AccessDeniedHandler` allows you to process t
 
 [[csrf-login]]
 ==== Logging In
-In order to protect against forging log in requests the log in form should be protected against CSRF attacks too. Since the `CsrfToken` is stored in HttpSession, this means an HttpSession will be created as soon as `CsrfToken` token attribute is accessed. While this sounds bad in a RESTful / stateless architecture the reality is that state is necessary to implement practical security. Without state, we have nothing we can do if a token is compromised. Practically speaking, the CSRF token is quite small in size and should have a negligible impact on our architecture.
+In order to protect against http://en.wikipedia.org/wiki/Cross-site_request_forgery#Forging_login_requests[forging log in requests] the log in form should be protected against CSRF attacks too. Since the `CsrfToken` is stored in HttpSession, this means an HttpSession will be created as soon as `CsrfToken` token attribute is accessed. While this sounds bad in a RESTful / stateless architecture the reality is that state is necessary to implement practical security. Without state, we have nothing we can do if a token is compromised. Practically speaking, the CSRF token is quite small in size and should have a negligible impact on our architecture.
 
 
 [[csrf-logout]]