feat: add feature flag to enable legacy md5 hash for anonymous user id

cms/envs/common.py

@@ -516,6 +516,17 @@
     #   in the LMS and CMS.
     # .. toggle_tickets: 'https://github.com/open-craft/edx-platform/pull/429'
     'DISABLE_UNENROLLMENT': False,
+
+    # .. toggle_name: FEATURES['ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID']
+    # .. toggle_implementation: DjangoSetting
+    # .. toggle_default: False
+    # .. toggle_description: Whether to enable the legacy MD5 hashing algorithm to generate anonymous user id
+    #   instead of the newer SHAKE128 hashing algorithm
+    # .. toggle_use_cases: open_edx
+    # .. toggle_creation_date: 2022-08-08
+    # .. toggle_target_removal_date: None
+    # .. toggle_tickets: 'https://github.com/openedx/edx-platform/pull/30832'
+    'ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID': False,
 }
 
 # .. toggle_name: ENABLE_COPPA_COMPLIANCE

common/djangoapps/student/models.py

@@ -215,12 +215,22 @@ def anonymous_id_for_user(user, course_id):
         # function: Rotate at will, since the hashes are stored and
         # will not change.
         # include the secret key as a salt, and to make the ids unique across different LMS installs.
-        hasher = hashlib.shake_128()
+        legacy_hash_enabled = settings.FEATURES.get('ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID', False)
+        if legacy_hash_enabled:
+            # Use legacy MD5 algorithm if flag enabled
+            hasher = hashlib.md5()
+        else:
+            hasher = hashlib.shake_128()
+
         hasher.update(settings.SECRET_KEY.encode('utf8'))
         hasher.update(str(user.id).encode('utf8'))
         if course_id:
             hasher.update(str(course_id).encode('utf-8'))
-        anonymous_user_id = hasher.hexdigest(16)  # pylint: disable=too-many-function-args
+
+        if legacy_hash_enabled:
+            anonymous_user_id = hasher.hexdigest()
+        else:
+            anonymous_user_id = hasher.hexdigest(16)  # pylint: disable=too-many-function-args
 
         try:
             AnonymousUserId.objects.create(

common/djangoapps/student/tests/tests.py

@@ -1057,6 +1057,17 @@ def test_anonymous_id_secret_key_changes_result_in_diff_values_for_same_new_user
             assert anonymous_id != new_anonymous_id
             assert self.user == user_by_anonymous_id(new_anonymous_id)
 
+    def test_enable_legacy_hash_flag(self):
+        """Test that different anonymous id returned if ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID enabled."""
+        CourseEnrollment.enroll(self.user, self.course.id)
+        anonymous_id = anonymous_id_for_user(self.user, self.course.id)
+        with patch.dict(settings.FEATURES, ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID=True):
+            # Recreate user object to clear cached anonymous id.
+            self.user = User.objects.get(pk=self.user.id)
+            AnonymousUserId.objects.filter(user=self.user).filter(course_id=self.course.id).delete()
+            new_anonymous_id = anonymous_id_for_user(self.user, self.course.id)
+            assert anonymous_id != new_anonymous_id
+
 
 @skip_unless_lms
 @patch('openedx.core.djangoapps.programs.utils.get_programs')

lms/envs/common.py

@@ -1018,6 +1018,17 @@
     # .. toggle_target_removal_date: None
     # .. toggle_tickets: 'https://openedx.atlassian.net/browse/MST-1458'
     'ENABLE_CERTIFICATES_IDV_REQUIREMENT': False,
+
+    # .. toggle_name: FEATURES['ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID']
+    # .. toggle_implementation: DjangoSetting
+    # .. toggle_default: False
+    # .. toggle_description: Whether to enable the legacy MD5 hashing algorithm to generate anonymous user id
+    #   instead of the newer SHAKE128 hashing algorithm
+    # .. toggle_use_cases: open_edx
+    # .. toggle_creation_date: 2022-08-08
+    # .. toggle_target_removal_date: None
+    # .. toggle_tickets: 'https://github.com/openedx/edx-platform/pull/30832'
+    'ENABLE_LEGACY_MD5_HASH_FOR_ANONYMOUS_USER_ID': False,
 }
 
 # Specifies extra XBlock fields that should available when requested via the Course Blocks API