$.ajax({
        username: login,
        password: pass,
        async : false,
        cache: "false",
        dataType: 'json',
        type: 'get',
        url: url,
        success: function(data){...}

beforeSend: function (xhr) {
     xhr.setRequestHeader('Authorization', makeBaseAuth(login, pass));
    }

var
  oWebModule: TWebModule;
  sBody: String;
begin
  oWebModule := GetDataSnapWebModule;
  sBody := oWebModule.Request.Content;
end;