code: def lookup_token(self):
          
          url = _url_joiner(self._vault_url, 'v1/auth/token/lookup-self')
          resp = requests.get(url, headers=self._headers)
          resp.raise_for_status()
          data = resp.json()
          if data.get('errors'):
              raise VaultException(u'Error looking up Vault token: {}'.format(data['errors']))
          return data
docs: Convenience method: look up the vault token