def access_token(self):
        """return an Oauth 2.0 Bearer access token if it can be found"""
        access_token = self.get_auth_bearer()
        if not access_token:
            access_token = self.query_kwargs.get('access_token', '')
            if not access_token:
                access_token = self.body_kwargs.get('access_token', '')

        return access_token