class RetrieveUserByField(RetrieveAPIView):
    serializer_class = UserSerializer

    def retrieve(self, request, *args, **kwargs):
        field = request.data.get('field')
        value = request.data.get('value')
        try:
            user = User.objects.filter(field=value)
            serializer = self.get_serializer(user)
            return JsonResponse(serializer)
        except User.DoesNotExist:
            return JsonResponse(None)