Implement kill-switch for the Learning MFE

by overriding can_load_courseware if the MFE is disabled for the user

If the user would be allowed to see the courseware MFE
(can_load_courseware), we check whether the MFE is disabled for them,
based on global settings, course settings (mongo courses), or their
particular bucketing in our ExperimentWaffleFlag.

If we determine they shouldn’t be allowed to see it, we return a new
CoursewareMicrofrontendDisabledAccessError access response, which the
MFE will use to know it should redirect to the old LMS experience.

Fixes: TNL-7362
Co-authored-by: stvn <stvn@mit.edu>

lms/djangoapps/courseware/access_response.py

@@ -236,3 +236,14 @@ class AuthenticationRequiredAccessError(AccessError):
         developer_message = u"User must be authenticated to view the course"
         user_message = _(u"You must be logged in to see this course")
         super(AuthenticationRequiredAccessError, self).__init__(error_code, developer_message, user_message)
+
+
+class CoursewareMicrofrontendDisabledAccessError(AccessError):
+    """
+    Access denied because the courseware micro-frontend is disabled for this user.
+    """
+    def __init__(self):
+        error_code = 'microfrontend_disabled'
+        developer_message = u'Micro-frontend is disabled for this user'
+        user_message = _(u'Please view your course in the existing experience')
+        super(CoursewareMicrofrontendDisabledAccessError, self).__init__(error_code, developer_message, user_message)

openedx/core/djangoapps/courseware_api/tests/test_views.py

@@ -81,7 +81,9 @@ class CourseApiTestViews(BaseCoursewareTests):
         (False, None, ACCESS_GRANTED),
     )
     @ddt.unpack
-    def test_course_metadata(self, logged_in, enrollment_mode, enable_anonymous):
+    @mock.patch('openedx.core.djangoapps.courseware_api.views.CoursewareMeta.is_microfrontend_enabled_for_user')
+    def test_course_metadata(self, logged_in, enrollment_mode, enable_anonymous, is_microfrontend_enabled_for_user):
+        is_microfrontend_enabled_for_user.return_value = True
         check_public_access = mock.Mock()
         check_public_access.return_value = enable_anonymous
         with mock.patch('lms.djangoapps.courseware.access_utils.check_public_access', check_public_access):

openedx/core/djangoapps/courseware_api/views.py

@@ -7,6 +7,7 @@ import json
 from babel.numbers import get_currency_symbol
 from completion.exceptions import UnavailableCompletionData
 from completion.utilities import get_key_to_last_completed_block
+from django.conf import settings
 from django.urls import reverse
 from edx_rest_framework_extensions.auth.jwt.authentication import JwtAuthentication
 from edx_rest_framework_extensions.auth.session.authentication import SessionAuthenticationAllowInactiveUser
@@ -20,10 +21,14 @@ from course_modes.models import CourseMode
 from edxnotes.helpers import is_feature_enabled
 from lms.djangoapps.course_api.api import course_detail
 from lms.djangoapps.courseware.access import has_access
+from lms.djangoapps.courseware.access_response import (
+    CoursewareMicrofrontendDisabledAccessError,
+)
 from lms.djangoapps.courseware.courses import check_course_access, get_course_by_id
 from lms.djangoapps.courseware.masquerade import setup_masquerade
 from lms.djangoapps.courseware.module_render import get_module_by_usage_id
 from lms.djangoapps.courseware.tabs import get_course_tab_list
+from lms.djangoapps.courseware.toggles import REDIRECT_TO_COURSEWARE_MICROFRONTEND
 from lms.djangoapps.courseware.utils import can_show_verified_upgrade
 from lms.djangoapps.courseware.utils import verified_upgrade_deadline_link
 from openedx.core.lib.api.view_utils import DeveloperErrorViewMixin
@@ -63,6 +68,34 @@ class CoursewareMeta:
     def __getattr__(self, name):
         return getattr(self.overview, name)
 
+    def is_microfrontend_enabled_for_user(self):
+        """
+        This method is the "opposite" of _redirect_to_learning_mfe in
+        lms/djangoapps/courseware/views/index.py. But not exactly...
+
+        1. It needs to respect the global
+           ENABLE_COURSEWARE_MICROFRONTEND feature flag and redirect users
+           out of the MFE experience if it's turned off.
+        2. It needs to redirect for old Mongo courses.
+        3. It does NOT need to worry about exams - the MFE will handle
+           those on its own. As of this writing, it will redirect back to
+           the LMS experience, but that may change soon.
+        4. Finally, it needs to redirect users who are bucketed out of
+           the MFE experience, but who aren't staff. Staff are allowed to
+           stay.
+        """
+        # REDIRECT: feature disabled globally
+        if not settings.FEATURES.get('ENABLE_COURSEWARE_MICROFRONTEND'):
+            return False
+        # REDIRECT: Old Mongo courses, until removed from platform
+        if self.course_key.deprecated:
+            return False
+        # REDIRECT: If the user isn't staff, redirect if they're bucketed into the old LMS experience.
+        if not self.original_user_is_staff and not REDIRECT_TO_COURSEWARE_MICROFRONTEND.is_enabled(self.course_key):
+            return False
+        # STAY: If the user has made it past all the above, they're good to stay!
+        return True
+
     @property
     def enrollment(self):
         """
@@ -107,7 +140,7 @@ class CoursewareMeta:
 
     @property
     def can_load_courseware(self):
-        return check_course_access(
+        access_response = check_course_access(
             self.overview,
             self.effective_user,
             'load',
@@ -115,6 +148,12 @@ class CoursewareMeta:
             check_survey_complete=False,
             check_if_authenticated=True,
         ).to_json()
+        # Only check whether the MFE is enabled if the user would otherwise be allowed to see it
+        # This means that if the user was denied access, they'll see a meaningful message first if
+        # there is one.
+        if access_response and not self.is_microfrontend_enabled_for_user():
+            return CoursewareMicrofrontendDisabledAccessError().to_json()
+        return access_response
 
     @property
     def tabs(self):