/** GET /activate -> activate the registered user. */
 @RequestMapping(
     value = "/activate",
     method = RequestMethod.GET,
     produces = MediaType.APPLICATION_JSON_VALUE)
 @Timed
 public ResponseEntity<String> activateAccount(@RequestParam(value = "key") String key) {
   User user = userService.activateRegistration(key);
   if (user == null) {
     return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
   }
   return new ResponseEntity<String>(HttpStatus.OK);
 }