Added CsrfMiddleware to contrib, and documentation.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@2868 bcc190cf-cafb-0310-a4f2-bffc1f526a37

2 files changed, 84 insertions, 0 deletions

diff --git a/django/contrib/csrf/__init__.py b/django/contrib/csrf/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/django/contrib/csrf/__init__.py
diff --git a/django/contrib/csrf/middleware.py b/django/contrib/csrf/middleware.py
new file mode 100644
index 0000000000..4c00461b89
--- /dev/null
+++ b/django/contrib/csrf/middleware.py
@@ -0,0 +1,84 @@
+"""
+Cross Site Request Forgery Middleware.
+
+This module provides a middleware that implements protection
+against request forgeries from other sites. 
+
+"""
+from django.conf import settings
+from django.http import HttpResponseForbidden
+import md5
+import re
+
+_ERROR_MSG = "<h1>403 Forbidden</h1><p>Cross Site Request Forgery detected.  Request aborted.</p>"
+
+_POST_FORM_RE = \
+    re.compile(r'(<form\W[^>]*\bmethod=(\'|"|)POST(\'|"|)\b[^>]*>)', re.IGNORECASE)
+    
+_HTML_TYPES = ('text/html', 'application/xhtml+xml')    
+
+def _make_token(session_id):
+    return md5.new(settings.SECRET_KEY + session_id).hexdigest()
+    
+class CsrfMiddleware(object):
+    """Django middleware that adds protection against Cross Site
+    Request Forgeries by adding hidden form fields to POST forms and 
+    checking requests for the correct value.  
+    
+    In the list of middlewares, SessionMiddleware is required, and must come 
+    after this middleware.  CsrfMiddleWare must come after compression 
+    middleware.
+   
+    If a session ID cookie is present, it is hashed with the SECRET_KEY 
+    setting to create an authentication token.  This token is added to all 
+    outgoing POST forms and is expected on all incoming POST requests that 
+    have a session ID cookie.
+    
+    If you are setting cookies directly, instead of using Django's session 
+    framework, this middleware will not work.
+    """
+    
+    def process_request(self, request):
+        if request.POST:
+            try:
+                session_id = request.COOKIES[settings.SESSION_COOKIE_NAME]
+            except KeyError:
+                # No session, no check required
+                return None
+
+            csrf_token = _make_token(session_id)
+            # check incoming token
+            try:
+                request_csrf_token = request.POST['csrfmiddlewaretoken']
+            except KeyError:
+                return HttpResponseForbidden(_ERROR_MSG)
+            
+            if request_csrf_token != csrf_token:
+                return HttpResponseForbidden(_ERROR_MSG)
+                
+        return None
+        
+    def process_response(self, request, response):
+        csrf_token = None
+        try:
+            cookie = response.cookies[settings.SESSION_COOKIE_NAME]
+            csrf_token = _make_token(cookie.value)
+        except KeyError:
+            # No outgoing cookie to set session, but 
+            # a session might already exist.
+            try:
+                session_id = request.COOKIES[settings.SESSION_COOKIE_NAME]
+                csrf_token = _make_token(session_id)
+            except KeyError:
+                # no incoming or outgoing cookie
+                pass
+            
+        if csrf_token is not None and \
+           response['Content-Type'].split(';')[0] in _HTML_TYPES:
+           
+            # Modify any POST forms
+            extra_field = "<div style='display:none;'>" + \
+                "<input type='hidden' name='csrfmiddlewaretoken' value='" + \
+                csrf_token + "' /></div>"
+            response.content = _POST_FORM_RE.sub('\\1' + extra_field, response.content)
+        return response