'Invalidates a used request token.
:param client_key: The client/consumer key.
:param request_token: The request token string.
:param request: An oauthlib.common.Request object.
:returns: None
Per `Section 2.3`__ of the spec:
"The server MUST (...) ensure that the temporary
credentials have not expired or been used before."
.. _`Section 2.3`: http://tools.ietf.org/html/rfc5849#section-2.3
This method should ensure that provided token won\'t validate anymore.
It can be simply removing RequestToken from storage or setting
specific flag that makes it invalid (note that such flag should be
also validated during request token validation).
This method is used by
* AccessTokenEndpoint'

def invalidate_request_token(self, client_key, request_token, request):

    raise NotImplementedError(u'Subclasses    must    implement    this    function.')
