Initial commit for default DRF FilterBackend on full Open edX API

Attempting to handle multi-tenancy protections for full API.
https://appsembler.atlassian.net/browse/ENG-176

openedx/core/djangoapps/appsembler/openedx_api/filters.py

@@ -0,0 +1,110 @@
+"""
+Default filter backend for full DRF API.
+
+Set via  REST_FRAMEWORK settings
+
+REST_FRAMEWORK = {
+    'DEFAULT_FILTER_BACKENDS': [
+        'openedx.core.djangoapps.appsembler.openedx_api.filters.AppsemblerMultiTenantFilterBackend'
+    ]
+}
+
+Implement django_filters Filterset to provide a final filter by
+allowed course Organization to ensure multitenant-safe API results.
+
+..
+The APIs we want to support are (draft):
+see https://courses.edx.org/api-docs/
+
+Certificates (GeneratedCertificate.course_id__org)
+Cohorts (CourseUserGroup.course_id -> no FK to courseoverview)
+Completion (BlockCompletion.course_id__org)
+? Course Experience ()
+? Course Home ()
+Courses (CourseOverview.org)        
+Courseware (CourseOverview.org)
+Discussion (not sure how to handle... discussions aren't Django objs, just gets course via lms.djangoapps.courseware.courses.get_course_with_access)
+Enrollment (CourseEnrollment.course__org)
+Grades:  not sure yet how these are serialized... 
+...or if they use PersistentGrades.         
+User (User.organizations__contains)
+...
+
+"""
+
+from django.contrib.auth.models import User
+
+from django_filters import rest_framework as filters
+from django_filters import rest_framework  
+
+from completion.models import BlockCompletion
+from lms.djangoapps.content.course_overviews.models import CourseOverview
+from lms.djangoapps.certificates.models import GeneratedCertificate
+from organizations.models import Organization
+from student.models import CourseEnrollment
+
+
+COURSE_PREFIX = 'course-v1:'
+
+
+# TODO: Need to figure out how to limit this FilterBackend (or make essentially no-op) for some parts of API 
+
+
+class AppsemblerMultiTenantFilterBackend(filters.DjangoFilterBackend):
+
+    filterset_base = AllowedCourseOrgFilterSet
+
+
+class AllowedCourseOrgFilterSet(filters.FilterSet):
+    """Filter by allowed organization, with dynamic queryset filter. 
+    """
+    MODEL_COURSE_ORG_LOOKUPS = {
+      User: 'organizations__contains',
+      CourseEnrollment: 'course__org__',
+      CourseOverview: 'org',
+      CourseUserGroup: 'course_id__startswith',
+      GeneratedCertificate: 'course_id__startswith',
+      BlockCompletion: 'context_key__startswith',
+      ...
+    }
+
+    # have no ForeignKey to CourseOverview or other path to Organization,
+    # just an OpaqueKeyField subclass so we have to do a string comparison
+    OPAQUE_KEY_FIELD_LOOKUP_MODELS = (
+      BlockCompletion,
+      CourseUserGroup, 
+      GeneratedCertificate, 
+    )
+
+    # org field is just a string of the name of the org.
+    STRING_ORG_NAME_LOOKUP_MODELS = (
+      CourseEnrollment,
+      CourseOverview,
+    )
+
+    # TODO: Allow a superuser to bypass filter
+
+    allowed_org = filters.BooleanFilter(method="filter_allowed_org")
+
+    def filter_allowed_org(self, queryset, name, value):
+        import pdb; pdb.set_trace()
+        requesting_user = self.request.user
+
+        try:
+          user_allowed_org = self.request.user.organizations.first()
+        except Organization.DoesNotExist:
+            raise  # TODO: do something else
+
+        try:
+            lookup = MODEL_COURSE_ORG_LOOKUPS[self.queryset.model]
+        except KeyError:
+            raise  # TODO: do something else
+
+        if model in OPAQUE_KEY_FIELD_LOOKUP_MODELS:
+            return queryset.filter(**{lookup: "{}{}+".format(COURSE_PREFIX, user_allowed_org))})
+        elif model in STRING_ORG_NAME_LOOKUP_MODELS:
+            return queryset.filter(**{lookup: user_allowed_org.short_name})        
+        else:
+            return queryset.filter(**{lookup: user_allowed_org})
+
+    # don't declare an explicit model via Meta

openedx/core/djangoapps/appsembler/settings/settings/common.py

@@ -89,3 +89,12 @@ def plugin_settings(settings):
 
     # Off by default. See the `site_configuration.tahoe_organization_helpers.py` module.
     settings.FEATURES['TAHOE_SITE_CONFIG_CLIENT_ORGANIZATIONS_SUPPORT'] = False
+
+    # Use default DRF API FilterBackend to handle multi-tenancy protections for Open edX API
+    settings.REST_FRAMEWORK.update(
+        {
+            'DEFAULT_FILTER_BACKENDS': [
+                'openedx.core.djangoapps.appsembler.openedx_api.filters.AppsemblerMultiTenantFilterBackend'
+            ]
+        }
+    )