Retrieve workitems thru Rest API : 200 code but no data retrieved

the HTML I get is :

<html >
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=10">
<title></title>

<link type="text/css" rel="stylesheet" href="/jazz/web/_style/?include=A~&etag=YoZXqQA7vM_en_GB&_proxyURL=%2Fjazz&ss=RzxVv">
<link rel="shortcut icon" href="/jazz/web/net.jazz.ajax/jazz.ico">

<style type="text/css">
#net-jazz-ajax-NoScriptMessage {
        width: 100%;
        color: #D0D0D0;
        font-size: 2em;
        text-align: center;
        position: absolute;
        top: 1%;
        z-index: 999;
}
</style>

</head>

<body class="claro">
        <noscript><div id="net-jazz-ajax-NoScriptMessage">Javascript is either disabled or not available in your Browser</div></noscript>
        <div id="net-jazz-ajax-InitialLoadMessage">Loading...</div>
        <div id="net-jazz-ajax-WorkbenchRoot"></div>

        <script type="text/javascript">
                djConfig = {
                        isDebug: false,
                        layout: "",
                        usePlainJson: true,
                        baseUrl: "/jazz/web/dojo/",
                        locale: "en-gb",
                        localizationComplete: true
                };
                /null/
                net = {jazz: {ajax: {}}};
                net.jazz.ajax._contextRoot = "/jazz";
                net.jazz.ajax._appPath = "/jazz/auth/authrequired";
                net.jazz.ajax._webuiPrefix = "/web/";
        </script>

        <script type="text/javascript" src="/jazz/web/_js/?include=A~&etag=YoZXqQA7vM_en_GB&_proxyURL=%2Fjazz&ss=RzxVv&locale=en-gb"></script>

<script type="text/javascript">
require("dojo/main").getObject('jazz.core.loader', true)._serverStartup="RzxVv";
require("dojo/main").getObject('jazz.core.loader',true)._loaded=["A"];
</script>


        <script type="text/javascript">
        / <![CDATA[ /
                dojo.addOnLoad( function() {
                        net.jazz.ajax.ui.PlatformUI.createAndRunWorkbench("net.jazz.web.app.authrequired");
                });
        / ]]> /
        </script>
</body>
</html>