Comment by arboroia

You're close, but that first endpoint is just to retrieve the auth URL, no need to post anything to it. It then passes the seed and password to the returned URL, so: "http://35.246.158.51:8070/auth/v2" gets '{"Seed": "xxx", "Password": "xxx"}' of some kind

I haven't yet figured out what those are though...

See:

  Future<Token> login(String seed, String password) {
    var headers = new Map<String,String>();
      return _netUtil.get(LOGIN_URL, headers:headers).then((dynamic authUrl) {
      try {
        if (authUrl == null) {
          return Future<Token>.sync(() => new Token("", false, 0));
        }
        var loginUrl = BASE_URL + AuthURL.map(json.decode(authUrl.body)).url;