public static string username='admin';

 public static string password='N3xxxxxxxxx';

 @HttpPost

global static void postItems()
    {
   Http http = new Http();
        HttpRequest req = new HttpRequest();
        req.setEndpoint('https://xxxx.nexenta.com/rest/api/2/search?jql='+
                        'issuekey=' + jirakey +
                        '&os_username=' + username +
                        '&os_password=' + password +
                        '&expand=' + change );
        req.setMethod('GET');
        HttpResponse res = http.send(req);
        System.debug('JSON Response: ' + res.getBody());
}