Pass an ID to frontend from the server

Question

I am building a web app and I need to pass the user's id to my front-end(angular) so I can do some ajax calls.

My question is, how can I give(store) the user's id to my front end? For example, a user can create a group by specifying a group name, but I need to be able to pass the users Id aswell in my ajax request(My backend endpoint needs both an Id and a name).

Angular:

    $scope.createGroup = function() {
            $http.post(BASE_URL + "/group", $scope.groupRequest).
                success(function (data, status, headers, config) {
                  console.log("Success");
                }).error(function(data, status, headers, config) {
                   $log.info("Error: status =" + status + ", body =" + JSON.stringify(data));
                });
        }

Front-end controller

     @RequestMapping(value = "/group", method = RequestMethod.POST)
public ResponseEntity createGroup(@RequestBody Map body) {
    try {
        return restTemplate.postForEntity(URI.create(BASE_URL + "/group"), body, Map.class);
    } catch (HttpClientErrorException e) {
        LOG.warn("Error when trying to fetch groups", e);
        return ResponseEntity.badRequest().body(e.getResponseBodyAsString());
    }
}

Java Back end controller

    @RequestMapping(value = "/group", method = RequestMethod.POST)
public ResponseEntity createGroup(@RequestBody @Valid GroupRequest groupRequest, BindingResult validation) {
    if (validation.hasErrors()) {
        throw new ValidationException(validation.getFieldErrors());
    }
    Long groupId = groupService.createGroup(groupRequest);
    URI groupLocationURI = URI.create("/group/" + groupId);
    return ResponseEntity.created(groupLocationURI).build();
}

Thanks