<html>
  <head>
    <script>
      function onGet() {
        var xhr = prepareRequest("GET");
        xhr.send();
      }

      function prepareRequest(method) {
        var url = document.getElementById("url");
        var user = document.getElementById("user");
        var password = document.getElementById("password");
        var body = document.getElementById("body");
        var xhr = new XMLHttpRequest();
        xhr.open(method, url.value, false);
        xhr.setRequestHeader("Authorization", "Basic " + window.btoa(user.value + ":" + password.value));
        xhr.setRequestHeader("Accept", "application/xml");
        xhr.setRequestHeader("Content-Type", "application/xml");
        xhr.onload = function (e) {
          var text = xhr.responseText;
          body.value = text;
        };
        return xhr;
      }
    </script>
  </head>
  <body>
    <form action="">
     <table>
       <tr>
         <td>URL</td>
         <td><input id="url" type="text" value="https://fedora.example.com/ovirt-engine/api"/></td>
       </tr>
       <tr>
         <td>User</td>
         <td><input id="user" type="text" value="admin@internal"/></td>
       </tr>
       <tr>
         <td>Password</td>
         <td><input id="password" type="password" value=""/></td>
       </tr>
       <tr>
         <td colspan="2">
           <div>
             Body
           </div>
           <div>
             <textarea id="body" rows="10" cols="80">
             </textarea>
           </div>
         </td>
       </tr>
       <tr>
        <td colspan="2">
          <input type="button" value="GET" onclick="onGet()"/>
       </tr>
     </table>
    </form>
  </body>
</html>