code: def _fetch_app_role_token(vault_url, role_id, secret_id):
          
          url = _url_joiner(vault_url, 'v1/auth/approle/login')
          resp = requests.post(url, data={'role_id': role_id, 'secret_id': secret_id})
          resp.raise_for_status()
          data = resp.json()
          if data.get('errors'):
              raise VaultException(u'Error fetching Vault token: {}'.format(data['errors']))
          return data['auth']['client_token']
docs: Get a Vault token, using the RoleID and SecretID