Add LTI Tool grading for Acos server assignments

When the A+ LTI Tool v1.3 feature was added in v1.18,
there was no support yet for the LTI grading of Acos server
assignments. Now, those grades can be sent to the LTI Platform.

Short description of the implementation:

- When the A+ front retrieves the exercise description from
  the exercise service, the HTTP GET request includes an extra
  parameter `lti_launch_id` if the user's current session includes
  LTI parameters from an LTI v1.3 launch (to A+ as the LTI Tool).
- The Aplus protocol at the Acos server
  (acos-server/acos-aplus#8) is modified
  so that it will store the LTI launch id parameter in
  the user's browser in a hidden HTML  `<input>` element.
- Acos server forwards the LTI launch parameter to the A+ front
  when the exercise submission is sent to the Acos server.
- When A+ receives the graded submission from the Acos server,
  A+ stores the LTI launch id in the submission `meta_data` field.
  The LTI launch id is then used to send the grade to
  the LTI Platform.

Fixes #1154

Author: murhum1

exercise/async_views.py

@@ -52,6 +52,12 @@ def _post_async_submission(request, exercise, submission, errors=None):
         submission.feedback = form.cleaned_data["feedback"]
         submission.grading_data = post_data
 
+        # Acos-submissions initialize this as an empty string for some reason; fix here
+        if submission.meta_data == "":
+            submission.meta_data = {}
+        if form.cleaned_data["lti_launch_id"]:
+            submission.meta_data["lti-launch-id"] = form.cleaned_data["lti_launch_id"]
+
         if form.cleaned_data["error"]:
             submission.set_error()
         else:

exercise/exercise_models.py

@@ -955,7 +955,7 @@ def get_load_url(
             )
             return self._build_service_url(
                 language, students,
-                ordinal, url_name, submission_url
+                ordinal, url_name, submission_url, lti_launch_id=request.session.get("lti-launch-id")
             )
         return super().get_load_url(language, request, students, url_name, ordinal)
 
@@ -994,20 +994,23 @@ def modify_post_parameters(self, data, files, user, students, request, url):
         """
         pass
 
-    def _build_service_url(self, language, students, ordinal_number, url_name, submission_url):
+    def _build_service_url(self, language, students, ordinal_number, url_name, submission_url, lti_launch_id=None):
         """
         Generates complete URL with added parameters to the exercise service.
         """
         uid_str = '-'.join(sorted(str(profile.user.id) for profile in students)) if students else ''
-        return update_url_params(self.get_service_url(language), {
+        params = {
             "max_points": self.max_points,
             "max_submissions": self.max_submissions,
             "submission_url": build_aplus_url(submission_url),
             "post_url": build_aplus_url(str(self.get_url(url_name)), user_url=True),
             "uid": uid_str,
             "ordinal_number": ordinal_number,
             "lang": language,
-        })
+        }
+        if lti_launch_id:
+            params["lti_launch_id"] = lti_launch_id
+        return update_url_params(self.get_service_url(language), params)
 
     @property
     def can_regrade(self):

exercise/forms.py

@@ -20,6 +20,7 @@ class SubmissionCallbackForm(forms.Form):
     feedback = forms.CharField(required=False)
     notify = forms.CharField(required=False)
     grading_payload = forms.CharField(required=False)
+    lti_launch_id = forms.CharField(required=False)
     error = forms.BooleanField(required=False)
 
     def clean(self):