Merge pull request #3954 from edx/brian/fix_session_id

Encrypt the session id before writing to tracking logs.

common/djangoapps/track/middleware.py

+import hmac
+import hashlib
 import json
 import re
 import logging
@@ -111,12 +113,26 @@ class TrackMiddleware(object):
         )
 
     def get_session_key(self, request):
-        """Gets the Django session key from the request or an empty string if it isn't found"""
+        """ Gets and encrypts the Django session key from the request or an empty string if it isn't found."""
         try:
-            return request.session.session_key
+            return self.encrypt_session_key(request.session.session_key)
         except AttributeError:
             return ''
 
+    def encrypt_session_key(self, session_key):
+        """Encrypts a Django session key to another 32-character hex value."""
+        if not session_key:
+            return ''
+
+        # Follow the model of django.utils.crypto.salted_hmac() and
+        # django.contrib.sessions.backends.base._hash() but use MD5
+        # instead of SHA1 so that the result has the same length (32)
+        # as the original session_key.
+        key_salt = "common.djangoapps.track" + self.__class__.__name__
+        key = hashlib.md5(key_salt + settings.SECRET_KEY).digest()
+        encrypted_session_key = hmac.new(key, msg=session_key, digestmod=hashlib.md5).hexdigest()
+        return encrypted_session_key
+
     def get_user_primary_key(self, request):
         """Gets the primary key of the logged in Django user"""
         try:

common/djangoapps/track/tests/test_middleware.py

@@ -117,12 +117,20 @@ class TrackMiddlewareTestCase(TestCase):
         SessionMiddleware().process_request(request)
         request.session.save()
         session_key = request.session.session_key
-
+        expected_session_key = self.track_middleware.encrypt_session_key(session_key)
+        self.assertEquals(len(session_key), len(expected_session_key))
         context = self.get_context_for_request(request)
         self.assert_dict_subset(context, {
-            'session': session_key,
+            'session': expected_session_key,
         })
 
+    @override_settings(SECRET_KEY='85920908f28904ed733fe576320db18cabd7b6cd')
+    def test_session_key_encryption(self):
+        session_key = '665924b49a93e22b46ee9365abf28c2a'
+        expected_session_key = '3b81f559d14130180065d635a4f35dd2'
+        encrypted_session_key = self.track_middleware.encrypt_session_key(session_key)
+        self.assertEquals(encrypted_session_key, expected_session_key)
+
     def test_request_headers(self):
         ip_address = '10.0.0.0'
         user_agent = 'UnitTest/1.0'

common/djangoapps/track/tests/test_views.py

@@ -7,6 +7,8 @@ from freezegun import freeze_time
 from django.test import TestCase
 from django.test.client import RequestFactory
 
+from eventtracking import tracker
+
 from datetime import datetime
 expected_time = datetime(2013, 10, 3, 8, 24, 55)
 
@@ -34,11 +36,12 @@ class TestTrackViews(TestCase):
             'event_type': sentinel.event_type,
             'event': {}
         })
-        views.user_track(request)
+        with tracker.get_tracker().context('edx.request', {'session': sentinel.session}):
+            views.user_track(request)
 
         expected_event = {
             'username': 'anonymous',
-            'session': '',
+            'session': sentinel.session,
             'ip': '127.0.0.1',
             'event_source': 'browser',
             'event_type': str(sentinel.event_type),
@@ -50,6 +53,7 @@ class TestTrackViews(TestCase):
             'context': {
                 'course_id': 'foo/bar/baz',
                 'org_id': 'foo',
+                'session': sentinel.session,
             },
         }
         self.mock_tracker.send.assert_called_once_with(expected_event)

common/djangoapps/track/views.py

@@ -41,18 +41,13 @@ def user_track(request):
     except:
         username = "anonymous"
 
-    try:
-        scookie = request.META['HTTP_COOKIE']  # Get cookies
-        scookie = ";".join([c.split('=')[1] for c in scookie.split(";") if "sessionid" in c]).strip()  # Extract session ID
-    except:
-        scookie = ""
-
     page = request.REQUEST['page']
 
     with eventtracker.get_tracker().context('edx.course.browser', contexts.course_context_from_url(page)):
+        context = eventtracker.get_tracker().resolve_context()
         event = {
             "username": username,
-            "session": scookie,
+            "session": context.get('session', ''),
             "ip": _get_request_header(request, 'REMOTE_ADDR'),
             "event_source": "browser",
             "event_type": request.REQUEST['event_type'],
@@ -61,7 +56,7 @@ def user_track(request):
             "page": page,
             "time": datetime.datetime.utcnow(),
             "host": _get_request_header(request, 'SERVER_NAME'),
-            "context": eventtracker.get_tracker().resolve_context(),
+            "context": context,
         }
 
     log_event(event)