diff --git a/lms/djangoapps/instructor/views/api.py b/lms/djangoapps/instructor/views/api.py
index ae6dd88f8bf0..fffd70d326d0 100644
--- a/lms/djangoapps/instructor/views/api.py
+++ b/lms/djangoapps/instructor/views/api.py
@@ -106,7 +106,9 @@
 from lms.djangoapps.instructor_task.api_helper import AlreadyRunningError, QueueConnectionError
 from lms.djangoapps.instructor_task.data import InstructorTaskTypes
 from lms.djangoapps.instructor_task.models import ReportStore
-from lms.djangoapps.instructor.views.serializer import RoleNameSerializer, UserSerializer
+from lms.djangoapps.instructor.views.serializer import (
+    RoleNameSerializer, UserSerializer, ShowStudentExtensionSerializer
+)
 from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
 from openedx.core.djangoapps.course_groups.cohorts import add_user_to_cohort, is_course_cohorted
 from openedx.core.djangoapps.course_groups.models import CourseUserGroup
@@ -2961,20 +2963,6 @@ def show_unit_extensions(request, course_id):
     return JsonResponse(dump_block_extensions(course, unit))
 
 
-class ShowStudentExtensionSerializer(serializers.Serializer):
-    """
-    Serializer for validating and processing the student identifier.
-    """
-    student = serializers.CharField(write_only=True, required=True)
-    def validate(self, data):
-        """
-        Validates the student identifier and converts it to a student object.
-        """
-        student_identifier = data.get('student')
-        data['student'] = require_student_from_identifier(student_identifier)
-        return data
-
-
 @method_decorator(cache_control(no_cache=True, no_store=True, must_revalidate=True), name='dispatch')
 # @method_decorator(handle_dashboard_error)
 class ShowStudentExtensions(APIView):
@@ -2982,11 +2970,6 @@ class ShowStudentExtensions(APIView):
     Shows all of the due date extensions granted to a particular student in a
     particular course.
     """
-    authentication_classes = (
-        JwtAuthentication,
-        BearerAuthenticationAllowInactiveUser,
-        SessionAuthenticationAllowInactiveUser,
-    )
     permission_classes = (IsAuthenticated, permissions.InstructorPermission)
     serializer_class = ShowStudentExtensionSerializer
     permission_name = permissions.GIVE_STUDENT_EXTENSION
@@ -2998,6 +2981,7 @@ def post(self, request, course_id):
             'student': request.data.get('student')
         }
         serializer = self.serializer_class(data=data)
+
         serializer.is_valid(raise_exception=True)
         student = serializer.validated_data['student']
         course = get_course_by_id(CourseKey.from_string(course_id))
diff --git a/lms/djangoapps/instructor/views/serializer.py b/lms/djangoapps/instructor/views/serializer.py
index b4f6f7626013..6b47a6d06cd0 100644
--- a/lms/djangoapps/instructor/views/serializer.py
+++ b/lms/djangoapps/instructor/views/serializer.py
@@ -7,6 +7,8 @@
 
 from lms.djangoapps.instructor.access import ROLES
 
+from .tools import get_student_from_identifier
+
 
 class RoleNameSerializer(serializers.Serializer):  # pylint: disable=abstract-method
     """
@@ -28,3 +30,24 @@ class UserSerializer(serializers.ModelSerializer):
     class Meta:
         model = User
         fields = ['username', 'email', 'first_name', 'last_name']
+
+
+class ShowStudentExtensionSerializer(serializers.Serializer):
+    """
+    Serializer for validating and processing the student identifier.
+    """
+    student = serializers.CharField(write_only=True, required=True)
+    def validate_student(self, value):
+        """
+        Validate that the student corresponds to an existing user.
+        """
+        try:
+            user = get_student_from_identifier(value)
+        except User.DoesNotExist:
+            response_payload = {
+                'student': value,
+                'userDoesNotExist': True,
+            }
+            return response_payload
+
+        return user