def validate_request(request):
    """
    Make sure the request is from Twilio and is valid.
    Ref: https://www.twilio.com/docs/security#validating-requests
    """

    # Forgot where this token if from. Different from above.
    # From: https://www.twilio.com/user/account/developer-tools/test-credentials
    # Should probably use TWILIO_AUTH_TOKEN once testing complete.
    auth_token = '9ea8a4f0ac5fd659fef71719e480c3c0'
    if 'HTTP_X_TWILIO_SIGNATURE' not in request.META:
        return 'X_TWILIO_SIGNATURE header is missing ' \
            'from request, not a valid Twilio request.'
        
        validator = RequestValidator(auth_token)
        
        if not validator.validate(
                request.build_absolute_uri(), 
                request.POST, 
                request.META['HTTP_X_TWILIO_SIGNATURE']):
            return 'Twilio request is not valid.'