public async Task<string> Auth(string login, string pass, string certpath, string appkey)
        {
                var username = login;
                var appKey = appkey;
                var certFilename = certpath;
                var password = pass;

                var client = new AuthClient(appKey);

                    var resp = await client.doLogin(username, password, certFilename);
                    if (resp.LoginStatus == "SUCCESS")
                    {
                        return resp.SessionToken;
                    }
                    else { return null; }
            }