Gets the AuthorizationSession for the default (bootstrap) typed Vault

        Assumes only one vault of this Type, but it can have children depending on underlying impl.

def _get_authz_session(self):
        """Gets the AuthorizationSession for the default (bootstrap) typed Vault

        Assumes only one vault of this Type, but it can have children depending on underlying impl.

        """
        from ..utilities import BOOTSTRAP_VAULT_TYPE
        try:
            vaults = self._get_vault_lookup_session().get_vaults_by_genus_type(BOOTSTRAP_VAULT_TYPE)
        except Unimplemented:
            return self._get_authz_manager().get_authorization_session()
        if vaults.available():
            vault = vaults.next()
            return self._get_authz_manager().get_authorization_session_for_vault(vault.get_id())
        else:
            return self._get_authz_manager().get_authorization_session()