Return a string representation of the OPTIONAL key-value pairs that can be sent with an OAUTHBEARER
        initial request.

def _token_extensions(self):
        """
        Return a string representation of the OPTIONAL key-value pairs that can be sent with an OAUTHBEARER
        initial request.
        """
        token_provider = self.config['sasl_oauth_token_provider']

        # Only run if the #extensions() method is implemented by the clients Token Provider class
        # Builds up a string separated by \x01 via a dict of key value pairs
        if callable(getattr(token_provider, "extensions", None)) and len(token_provider.extensions()) > 0:
            msg = "\x01".join(["{}={}".format(k, v) for k, v in token_provider.extensions().items()])
            return "\x01" + msg
        else:
            return ""