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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 _require_auth(fnc):
 """Authentication decorator."""

    @wraps(fnc)
    @_assure_identity
    def _wrapped(*args, **kwargs):
        if not identity.authenticated:
            msg = "Authentication required before calling '%s'." % fnc.__name__
            raise exc.NotAuthenticated(msg)
        return fnc(*args, **kwargs)
    return _wrapped