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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 check_key(request):
    '''
        POST endpoint determining whether or not a key exists and is valid
    '''
    api_objs = list(Api.objects.filter(name=request.POST['api']))
    if not api_objs:
        return HttpResponseBadRequest('Must specify valid API')

    # check the signature
    if get_signature(request.POST, api_objs[0].signing_key) != request.POST['signature']:
        return HttpResponseBadRequest('bad signature')

    get_object_or_404(Key, key=request.POST['key'], status='A')

    return HttpResponse('OK')