Create and save a new request token.

        :param request: OAuthlib request.
        :type request: oauthlib.common.Request
        :param credentials: A dict of extra token credentials.
        :returns: The verifier as a dict.

def create_verifier(self, request, credentials):
        """Create and save a new request token.

        :param request: OAuthlib request.
        :type request: oauthlib.common.Request
        :param credentials: A dict of extra token credentials.
        :returns: The verifier as a dict.
        """
        verifier = {
            'oauth_token': request.resource_owner_key,
            'oauth_verifier': self.token_generator(),
        }
        verifier.update(credentials)
        self.request_validator.save_verifier(
            request.resource_owner_key, verifier, request)
        return verifier