POST /as/token.oauth2 HTTP/1.1
  Host: authorization-server.example.com
  Authorization: Basic czZCaGRSa3F0Mzpoc3FFelFsVW9IQUU5cHg0RlNyNHlJ
  Content-Type: application/x-www-form-urlencoded

  grant_type=refresh_token
  &refresh_token=4LTC8lb0acc6Oy4esc1Nk9BWC0imAwH7kic16BDC2
  &resource=https%3A%2F%2Fcontacts.example.com%2F