<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def proxy_callback(request):
 """Handles CAS 2.0+ XML-based proxy callback call. Stores the proxy granting ticket in the database for future use. NB: Use created and set it in python in case database has issues with setting up the default timestamp value """


    pgtIou = request.GET.get('pgtIou')
    tgt = request.GET.get('pgtId')

    if not (pgtIou and tgt):
        logger.info('No pgtIou or tgt found in request.GET')
        return HttpResponse('No pgtIOO', content_type="text/plain")

    try:
        PgtIOU.objects.create(tgt=tgt, pgtIou=pgtIou, created=datetime.datetime.now())
        request.session['pgt-TICKET'] = pgtIou
        return HttpResponse('PGT ticket is: {ticket}'.format(ticket=pgtIou), content_type="text/plain")
    except Exception as e:
        logger.warning('PGT storage failed. {message}'.format(
            message=e
        ))
        return HttpResponse('PGT storage failed for {request}'.format(request=str(request.GET)),
                            content_type="text/plain")