def get_referer(self, request):
    """
    Retrieves the referer value for the current request
    being used for the handling.
    The referer value shall not be trusted as it may not
    be defined in the request.

    :type request: Request
    :param request: The request to be used.
    :rtype: String
    :return: The retrieved referer value (URL).
    """

    # retrieves the "referer" header and returns
    # the same value to the caller method
    referer_header = request.get_header("Referer")
    return referer_header