add external_user_key to response and add ability to search by username, email, or external user key

Code review comments - EDUCATOR-4319

undoing changes temporarily

undoing changes temporarily

Fixed exception handling

re-added changes after hard reset

removed waffle flag (wrong merge

removed waffle flag (wrong merge

common/djangoapps/student/models.py

@@ -1244,6 +1244,26 @@ class CourseEnrollment(models.Model):
         except cls.DoesNotExist:
             return None
 
+    @classmethod
+    def get_program_enrollment(cls, user, course_id):
+        """
+        Return the ProgramEnrollment associated with the CourseEnrollment specified
+        by the user and course_id.
+        Return None if there is no ProgramEnrollment.
+
+        Arguments:
+            user (User): the user for whom we want the program enrollment
+            coure_id (CourseKey): the id of the course the user has a course enrollment in
+
+        Returns:
+            ProgramEnrollment object or None
+        """
+        try:
+            course_enrollment = cls.objects.get(user=user, course_id=course_id)
+            return course_enrollment.programcourseenrollment.program_enrollment
+        except (ObjectDoesNotExist):
+            return None
+
     @classmethod
     def is_enrollment_closed(cls, user, course):
         """