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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def crl(request, pk):
 """ returns CRL of a CA """

    authenticated = request.user.is_authenticated
    authenticated = authenticated() if callable(authenticated) else authenticated
    if app_settings.CRL_PROTECTED and not authenticated:
        return HttpResponse(_('Forbidden'),
                            status=403,
                            content_type='text/plain')
    ca = crl.ca_model.objects.get(pk=pk)
    return HttpResponse(ca.crl,
                        status=200,
                        content_type='application/x-pem-file')